1.. SPDX-License-Identifier: (GPL-2.0+ OR CC-BY-4.0) 2.. See the bottom of this file for additional redistribution information. 3 4Reporting issues 5++++++++++++++++ 6 7 8The short guide (aka TL;DR) 9=========================== 10 11Are you facing a regression with vanilla kernels from the same stable or 12longterm series? One still supported? Then search the `LKML 13<https://lore.kernel.org/lkml/>`_ and the `Linux stable mailing list 14<https://lore.kernel.org/stable/>`_ archives for matching reports to join. If 15you don't find any, install `the latest release from that series 16<https://kernel.org/>`_. If it still shows the issue, report it to the stable 17mailing list (stable@vger.kernel.org) and CC the regressions list 18(regressions@lists.linux.dev); ideally also CC the maintainer and the mailing 19list for the subsystem in question. 20 21In all other cases try your best guess which kernel part might be causing the 22issue. Check the :ref:`MAINTAINERS <maintainers>` file for how its developers 23expect to be told about problems, which most of the time will be by email with a 24mailing list in CC. Check the destination's archives for matching reports; 25search the `LKML <https://lore.kernel.org/lkml/>`_ and the web, too. If you 26don't find any to join, install `the latest mainline kernel 27<https://kernel.org/>`_. If the issue is present there, send a report. 28 29The issue was fixed there, but you would like to see it resolved in a still 30supported stable or longterm series as well? Then install its latest release. 31If it shows the problem, search for the change that fixed it in mainline and 32check if backporting is in the works or was discarded; if it's neither, ask 33those who handled the change for it. 34 35**General remarks**: When installing and testing a kernel as outlined above, 36ensure it's vanilla (IOW: not patched and not using add-on modules). Also make 37sure it's built and running in a healthy environment and not already tainted 38before the issue occurs. 39 40If you are facing multiple issues with the Linux kernel at once, report each 41separately. While writing your report, include all information relevant to the 42issue, like the kernel and the distro used. In case of a regression, CC the 43regressions mailing list (regressions@lists.linux.dev) to your report. Also try 44to pin-point the culprit with a bisection; if you succeed, include its 45commit-id and CC everyone in the sign-off-by chain. 46 47Once the report is out, answer any questions that come up and help where you 48can. That includes keeping the ball rolling by occasionally retesting with newer 49releases and sending a status update afterwards. 50 51Step-by-step guide how to report issues to the kernel maintainers 52================================================================= 53 54The above TL;DR outlines roughly how to report issues to the Linux kernel 55developers. It might be all that's needed for people already familiar with 56reporting issues to Free/Libre & Open Source Software (FLOSS) projects. For 57everyone else there is this section. It is more detailed and uses a 58step-by-step approach. It still tries to be brief for readability and leaves 59out a lot of details; those are described below the step-by-step guide in a 60reference section, which explains each of the steps in more detail. 61 62Note: this section covers a few more aspects than the TL;DR and does things in 63a slightly different order. That's in your interest, to make sure you notice 64early if an issue that looks like a Linux kernel problem is actually caused by 65something else. These steps thus help to ensure the time you invest in this 66process won't feel wasted in the end: 67 68 * Are you facing an issue with a Linux kernel a hardware or software vendor 69 provided? Then in almost all cases you are better off to stop reading this 70 document and reporting the issue to your vendor instead, unless you are 71 willing to install the latest Linux version yourself. Be aware the latter 72 will often be needed anyway to hunt down and fix issues. 73 74 * Perform a rough search for existing reports with your favorite internet 75 search engine; additionally, check the archives of the `Linux Kernel Mailing 76 List (LKML) <https://lore.kernel.org/lkml/>`_. If you find matching reports, 77 join the discussion instead of sending a new one. 78 79 * See if the issue you are dealing with qualifies as regression, security 80 issue, or a really severe problem: those are 'issues of high priority' that 81 need special handling in some steps that are about to follow. 82 83 * Make sure it's not the kernel's surroundings that are causing the issue 84 you face. 85 86 * Create a fresh backup and put system repair and restore tools at hand. 87 88 * Ensure your system does not enhance its kernels by building additional 89 kernel modules on-the-fly, which solutions like DKMS might be doing locally 90 without your knowledge. 91 92 * Check if your kernel was 'tainted' when the issue occurred, as the event 93 that made the kernel set this flag might be causing the issue you face. 94 95 * Write down coarsely how to reproduce the issue. If you deal with multiple 96 issues at once, create separate notes for each of them and make sure they 97 work independently on a freshly booted system. That's needed, as each issue 98 needs to get reported to the kernel developers separately, unless they are 99 strongly entangled. 100 101 * If you are facing a regression within a stable or longterm version line 102 (say something broke when updating from 5.10.4 to 5.10.5), scroll down to 103 'Dealing with regressions within a stable and longterm kernel line'. 104 105 * Locate the driver or kernel subsystem that seems to be causing the issue. 106 Find out how and where its developers expect reports. Note: most of the 107 time this won't be bugzilla.kernel.org, as issues typically need to be sent 108 by mail to a maintainer and a public mailing list. 109 110 * Search the archives of the bug tracker or mailing list in question 111 thoroughly for reports that might match your issue. If you find anything, 112 join the discussion instead of sending a new report. 113 114After these preparations you'll now enter the main part: 115 116 * Unless you are already running the latest 'mainline' Linux kernel, better 117 go and install it for the reporting process. Testing and reporting with 118 the latest 'stable' Linux can be an acceptable alternative in some 119 situations; during the merge window that actually might be even the best 120 approach, but in that development phase it can be an even better idea to 121 suspend your efforts for a few days anyway. Whatever version you choose, 122 ideally use a 'vanilla' build. Ignoring these advices will dramatically 123 increase the risk your report will be rejected or ignored. 124 125 * Ensure the kernel you just installed does not 'taint' itself when 126 running. 127 128 * Reproduce the issue with the kernel you just installed. If it doesn't show 129 up there, scroll down to the instructions for issues only happening with 130 stable and longterm kernels. 131 132 * Optimize your notes: try to find and write the most straightforward way to 133 reproduce your issue. Make sure the end result has all the important 134 details, and at the same time is easy to read and understand for others 135 that hear about it for the first time. And if you learned something in this 136 process, consider searching again for existing reports about the issue. 137 138 * If your failure involves a 'panic', 'Oops', 'warning', or 'BUG', consider 139 decoding the kernel log to find the line of code that triggered the error. 140 141 * If your problem is a regression, try to narrow down when the issue was 142 introduced as much as possible. 143 144 * Start to compile the report by writing a detailed description about the 145 issue. Always mention a few things: the latest kernel version you installed 146 for reproducing, the Linux Distribution used, and your notes on how to 147 reproduce the issue. Ideally, make the kernel's build configuration 148 (.config) and the output from ``dmesg`` available somewhere on the net and 149 link to it. Include or upload all other information that might be relevant, 150 like the output/screenshot of an Oops or the output from ``lspci``. Once 151 you wrote this main part, insert a normal length paragraph on top of it 152 outlining the issue and the impact quickly. On top of this add one sentence 153 that briefly describes the problem and gets people to read on. Now give the 154 thing a descriptive title or subject that yet again is shorter. Then you're 155 ready to send or file the report like the MAINTAINERS file told you, unless 156 you are dealing with one of those 'issues of high priority': they need 157 special care which is explained in 'Special handling for high priority 158 issues' below. 159 160 * Wait for reactions and keep the thing rolling until you can accept the 161 outcome in one way or the other. Thus react publicly and in a timely manner 162 to any inquiries. Test proposed fixes. Do proactive testing: retest with at 163 least every first release candidate (RC) of a new mainline version and 164 report your results. Send friendly reminders if things stall. And try to 165 help yourself, if you don't get any help or if it's unsatisfying. 166 167 168Reporting regressions within a stable and longterm kernel line 169-------------------------------------------------------------- 170 171This subsection is for you, if you followed above process and got sent here at 172the point about regression within a stable or longterm kernel version line. You 173face one of those if something breaks when updating from 5.10.4 to 5.10.5 (a 174switch from 5.9.15 to 5.10.5 does not qualify). The developers want to fix such 175regressions as quickly as possible, hence there is a streamlined process to 176report them: 177 178 * Check if the kernel developers still maintain the Linux kernel version 179 line you care about: go to the `front page of kernel.org 180 <https://kernel.org/>`_ and make sure it mentions 181 the latest release of the particular version line without an '[EOL]' tag. 182 183 * Check the archives of the `Linux stable mailing list 184 <https://lore.kernel.org/stable/>`_ for existing reports. 185 186 * Install the latest release from the particular version line as a vanilla 187 kernel. Ensure this kernel is not tainted and still shows the problem, as 188 the issue might have already been fixed there. If you first noticed the 189 problem with a vendor kernel, check a vanilla build of the last version 190 known to work performs fine as well. 191 192 * Send a short problem report to the Linux stable mailing list 193 (stable@vger.kernel.org) and CC the Linux regressions mailing list 194 (regressions@lists.linux.dev); if you suspect the cause in a particular 195 subsystem, CC its maintainer and its mailing list. Roughly describe the 196 issue and ideally explain how to reproduce it. Mention the first version 197 that shows the problem and the last version that's working fine. Then 198 wait for further instructions. 199 200The reference section below explains each of these steps in more detail. 201 202 203Reporting issues only occurring in older kernel version lines 204------------------------------------------------------------- 205 206This subsection is for you, if you tried the latest mainline kernel as outlined 207above, but failed to reproduce your issue there; at the same time you want to 208see the issue fixed in a still supported stable or longterm series or vendor 209kernels regularly rebased on those. If that the case, follow these steps: 210 211 * Prepare yourself for the possibility that going through the next few steps 212 might not get the issue solved in older releases: the fix might be too big 213 or risky to get backported there. 214 215 * Perform the first three steps in the section "Dealing with regressions 216 within a stable and longterm kernel line" above. 217 218 * Search the Linux kernel version control system for the change that fixed 219 the issue in mainline, as its commit message might tell you if the fix is 220 scheduled for backporting already. If you don't find anything that way, 221 search the appropriate mailing lists for posts that discuss such an issue 222 or peer-review possible fixes; then check the discussions if the fix was 223 deemed unsuitable for backporting. If backporting was not considered at 224 all, join the newest discussion, asking if it's in the cards. 225 226 * One of the former steps should lead to a solution. If that doesn't work 227 out, ask the maintainers for the subsystem that seems to be causing the 228 issue for advice; CC the mailing list for the particular subsystem as well 229 as the stable mailing list. 230 231The reference section below explains each of these steps in more detail. 232 233 234Reference section: Reporting issues to the kernel maintainers 235============================================================= 236 237The detailed guides above outline all the major steps in brief fashion, which 238should be enough for most people. But sometimes there are situations where even 239experienced users might wonder how to actually do one of those steps. That's 240what this section is for, as it will provide a lot more details on each of the 241above steps. Consider this as reference documentation: it's possible to read it 242from top to bottom. But it's mainly meant to skim over and a place to look up 243details how to actually perform those steps. 244 245A few words of general advice before digging into the details: 246 247 * The Linux kernel developers are well aware this process is complicated and 248 demands more than other FLOSS projects. We'd love to make it simpler. But 249 that would require work in various places as well as some infrastructure, 250 which would need constant maintenance; nobody has stepped up to do that 251 work, so that's just how things are for now. 252 253 * A warranty or support contract with some vendor doesn't entitle you to 254 request fixes from developers in the upstream Linux kernel community: such 255 contracts are completely outside the scope of the Linux kernel, its 256 development community, and this document. That's why you can't demand 257 anything such a contract guarantees in this context, not even if the 258 developer handling the issue works for the vendor in question. If you want 259 to claim your rights, use the vendor's support channel instead. When doing 260 so, you might want to mention you'd like to see the issue fixed in the 261 upstream Linux kernel; motivate them by saying it's the only way to ensure 262 the fix in the end will get incorporated in all Linux distributions. 263 264 * If you never reported an issue to a FLOSS project before you should consider 265 reading `How to Report Bugs Effectively 266 <https://www.chiark.greenend.org.uk/~sgtatham/bugs.html>`_, `How To Ask 267 Questions The Smart Way 268 <http://www.catb.org/esr/faqs/smart-questions.html>`_, and `How to ask good 269 questions <https://jvns.ca/blog/good-questions/>`_. 270 271With that off the table, find below the details on how to properly report 272issues to the Linux kernel developers. 273 274 275Make sure you're using the upstream Linux kernel 276------------------------------------------------ 277 278 *Are you facing an issue with a Linux kernel a hardware or software vendor 279 provided? Then in almost all cases you are better off to stop reading this 280 document and reporting the issue to your vendor instead, unless you are 281 willing to install the latest Linux version yourself. Be aware the latter 282 will often be needed anyway to hunt down and fix issues.* 283 284Like most programmers, Linux kernel developers don't like to spend time dealing 285with reports for issues that don't even happen with their current code. It's 286just a waste everybody's time, especially yours. Unfortunately such situations 287easily happen when it comes to the kernel and often leads to frustration on both 288sides. That's because almost all Linux-based kernels pre-installed on devices 289(Computers, Laptops, Smartphones, Routers, ���) and most shipped by Linux 290distributors are quite distant from the official Linux kernel as distributed by 291kernel.org: these kernels from these vendors are often ancient from the point of 292Linux development or heavily modified, often both. 293 294Most of these vendor kernels are quite unsuitable for reporting issues to the 295Linux kernel developers: an issue you face with one of them might have been 296fixed by the Linux kernel developers months or years ago already; additionally, 297the modifications and enhancements by the vendor might be causing the issue you 298face, even if they look small or totally unrelated. That's why you should report 299issues with these kernels to the vendor. Its developers should look into the 300report and, in case it turns out to be an upstream issue, fix it directly 301upstream or forward the report there. In practice that often does not work out 302or might not what you want. You thus might want to consider circumventing the 303vendor by installing the very latest Linux kernel core yourself. If that's an 304option for you move ahead in this process, as a later step in this guide will 305explain how to do that once it rules out other potential causes for your issue. 306 307Note, the previous paragraph is starting with the word 'most', as sometimes 308developers in fact are willing to handle reports about issues occurring with 309vendor kernels. If they do in the end highly depends on the developers and the 310issue in question. Your chances are quite good if the distributor applied only 311small modifications to a kernel based on a recent Linux version; that for 312example often holds true for the mainline kernels shipped by Debian GNU/Linux 313Sid or Fedora Rawhide. Some developers will also accept reports about issues 314with kernels from distributions shipping the latest stable kernel, as long as 315its only slightly modified; that for example is often the case for Arch Linux, 316regular Fedora releases, and openSUSE Tumbleweed. But keep in mind, you better 317want to use a mainline Linux and avoid using a stable kernel for this 318process, as outlined in the section 'Install a fresh kernel for testing' in more 319detail. 320 321Obviously you are free to ignore all this advice and report problems with an old 322or heavily modified vendor kernel to the upstream Linux developers. But note, 323those often get rejected or ignored, so consider yourself warned. But it's still 324better than not reporting the issue at all: sometimes such reports directly or 325indirectly will help to get the issue fixed over time. 326 327 328Search for existing reports, first run 329-------------------------------------- 330 331 *Perform a rough search for existing reports with your favorite internet 332 search engine; additionally, check the archives of the Linux Kernel Mailing 333 List (LKML). If you find matching reports, join the discussion instead of 334 sending a new one.* 335 336Reporting an issue that someone else already brought forward is often a waste of 337time for everyone involved, especially you as the reporter. So it's in your own 338interest to thoroughly check if somebody reported the issue already. At this 339step of the process it's okay to just perform a rough search: a later step will 340tell you to perform a more detailed search once you know where your issue needs 341to be reported to. Nevertheless, do not hurry with this step of the reporting 342process, it can save you time and trouble. 343 344Simply search the internet with your favorite search engine first. Afterwards, 345search the `Linux Kernel Mailing List (LKML) archives 346<https://lore.kernel.org/lkml/>`_. 347 348If you get flooded with results consider telling your search engine to limit 349search timeframe to the past month or year. And wherever you search, make sure 350to use good search terms; vary them a few times, too. While doing so try to 351look at the issue from the perspective of someone else: that will help you to 352come up with other words to use as search terms. Also make sure not to use too 353many search terms at once. Remember to search with and without information like 354the name of the kernel driver or the name of the affected hardware component. 355But its exact brand name (say 'ASUS Red Devil Radeon RX 5700 XT Gaming OC') 356often is not much helpful, as it is too specific. Instead try search terms like 357the model line (Radeon 5700 or Radeon 5000) and the code name of the main chip 358('Navi' or 'Navi10') with and without its manufacturer ('AMD'). 359 360In case you find an existing report about your issue, join the discussion, as 361you might be able to provide valuable additional information. That can be 362important even when a fix is prepared or in its final stages already, as 363developers might look for people that can provide additional information or 364test a proposed fix. Jump to the section 'Duties after the report went out' for 365details on how to get properly involved. 366 367Note, searching `bugzilla.kernel.org <https://bugzilla.kernel.org/>`_ might also 368be a good idea, as that might provide valuable insights or turn up matching 369reports. If you find the latter, just keep in mind: most subsystems expect 370reports in different places, as described below in the section "Check where you 371need to report your issue". The developers that should take care of the issue 372thus might not even be aware of the bugzilla ticket. Hence, check the ticket if 373the issue already got reported as outlined in this document and if not consider 374doing so. 375 376 377Issue of high priority? 378----------------------- 379 380 *See if the issue you are dealing with qualifies as regression, security 381 issue, or a really severe problem: those are 'issues of high priority' that 382 need special handling in some steps that are about to follow.* 383 384Linus Torvalds and the leading Linux kernel developers want to see some issues 385fixed as soon as possible, hence there are 'issues of high priority' that get 386handled slightly differently in the reporting process. Three type of cases 387qualify: regressions, security issues, and really severe problems. 388 389You deal with a regression if some application or practical use case running 390fine with one Linux kernel works worse or not at all with a newer version 391compiled using a similar configuration. The document 392Documentation/admin-guide/reporting-regressions.rst explains this in more 393detail. It also provides a good deal of other information about regressions you 394might want to be aware of; it for example explains how to add your issue to the 395list of tracked regressions, to ensure it won't fall through the cracks. 396 397What qualifies as security issue is left to your judgment. Consider reading 398Documentation/process/security-bugs.rst before proceeding, as it 399provides additional details how to best handle security issues. 400 401An issue is a 'really severe problem' when something totally unacceptably bad 402happens. That's for example the case when a Linux kernel corrupts the data it's 403handling or damages hardware it's running on. You're also dealing with a severe 404issue when the kernel suddenly stops working with an error message ('kernel 405panic') or without any farewell note at all. Note: do not confuse a 'panic' (a 406fatal error where the kernel stop itself) with a 'Oops' (a recoverable error), 407as the kernel remains running after the latter. 408 409 410Ensure a healthy environment 411---------------------------- 412 413 *Make sure it's not the kernel's surroundings that are causing the issue 414 you face.* 415 416Problems that look a lot like a kernel issue are sometimes caused by build or 417runtime environment. It's hard to rule out that problem completely, but you 418should minimize it: 419 420 * Use proven tools when building your kernel, as bugs in the compiler or the 421 binutils can cause the resulting kernel to misbehave. 422 423 * Ensure your computer components run within their design specifications; 424 that's especially important for the main processor, the main memory, and the 425 motherboard. Therefore, stop undervolting or overclocking when facing a 426 potential kernel issue. 427 428 * Try to make sure it's not faulty hardware that is causing your issue. Bad 429 main memory for example can result in a multitude of issues that will 430 manifest itself in problems looking like kernel issues. 431 432 * If you're dealing with a filesystem issue, you might want to check the file 433 system in question with ``fsck``, as it might be damaged in a way that leads 434 to unexpected kernel behavior. 435 436 * When dealing with a regression, make sure it's not something else that 437 changed in parallel to updating the kernel. The problem for example might be 438 caused by other software that was updated at the same time. It can also 439 happen that a hardware component coincidentally just broke when you rebooted 440 into a new kernel for the first time. Updating the systems BIOS or changing 441 something in the BIOS Setup can also lead to problems that on look a lot 442 like a kernel regression. 443 444 445Prepare for emergencies 446----------------------- 447 448 *Create a fresh backup and put system repair and restore tools at hand.* 449 450Reminder, you are dealing with computers, which sometimes do unexpected things, 451especially if you fiddle with crucial parts like the kernel of its operating 452system. That's what you are about to do in this process. Thus, make sure to 453create a fresh backup; also ensure you have all tools at hand to repair or 454reinstall the operating system as well as everything you need to restore the 455backup. 456 457 458Make sure your kernel doesn't get enhanced 459------------------------------------------ 460 461 *Ensure your system does not enhance its kernels by building additional 462 kernel modules on-the-fly, which solutions like DKMS might be doing locally 463 without your knowledge.* 464 465The risk your issue report gets ignored or rejected dramatically increases if 466your kernel gets enhanced in any way. That's why you should remove or disable 467mechanisms like akmods and DKMS: those build add-on kernel modules 468automatically, for example when you install a new Linux kernel or boot it for 469the first time. Also remove any modules they might have installed. Then reboot 470before proceeding. 471 472Note, you might not be aware that your system is using one of these solutions: 473they often get set up silently when you install Nvidia's proprietary graphics 474driver, VirtualBox, or other software that requires a some support from a 475module not part of the Linux kernel. That why your might need to uninstall the 476packages with such software to get rid of any 3rd party kernel module. 477 478 479Check 'taint' flag 480------------------ 481 482 *Check if your kernel was 'tainted' when the issue occurred, as the event 483 that made the kernel set this flag might be causing the issue you face.* 484 485The kernel marks itself with a 'taint' flag when something happens that might 486lead to follow-up errors that look totally unrelated. The issue you face might 487be such an error if your kernel is tainted. That's why it's in your interest to 488rule this out early before investing more time into this process. This is the 489only reason why this step is here, as this process later will tell you to 490install the latest mainline kernel; you will need to check the taint flag again 491then, as that's when it matters because it's the kernel the report will focus 492on. 493 494On a running system is easy to check if the kernel tainted itself: if ``cat 495/proc/sys/kernel/tainted`` returns '0' then the kernel is not tainted and 496everything is fine. Checking that file is impossible in some situations; that's 497why the kernel also mentions the taint status when it reports an internal 498problem (a 'kernel bug'), a recoverable error (a 'kernel Oops') or a 499non-recoverable error before halting operation (a 'kernel panic'). Look near 500the top of the error messages printed when one of these occurs and search for a 501line starting with 'CPU:'. It should end with 'Not tainted' if the kernel was 502not tainted when it noticed the problem; it was tainted if you see 'Tainted:' 503followed by a few spaces and some letters. 504 505If your kernel is tainted, study Documentation/admin-guide/tainted-kernels.rst 506to find out why. Try to eliminate the reason. Often it's caused by one these 507three things: 508 509 1. A recoverable error (a 'kernel Oops') occurred and the kernel tainted 510 itself, as the kernel knows it might misbehave in strange ways after that 511 point. In that case check your kernel or system log and look for a section 512 that starts with this:: 513 514 Oops: 0000 [#1] SMP 515 516 That's the first Oops since boot-up, as the '#1' between the brackets shows. 517 Every Oops and any other problem that happens after that point might be a 518 follow-up problem to that first Oops, even if both look totally unrelated. 519 Rule this out by getting rid of the cause for the first Oops and reproducing 520 the issue afterwards. Sometimes simply restarting will be enough, sometimes 521 a change to the configuration followed by a reboot can eliminate the Oops. 522 But don't invest too much time into this at this point of the process, as 523 the cause for the Oops might already be fixed in the newer Linux kernel 524 version you are going to install later in this process. 525 526 2. Your system uses a software that installs its own kernel modules, for 527 example Nvidia's proprietary graphics driver or VirtualBox. The kernel 528 taints itself when it loads such module from external sources (even if 529 they are Open Source): they sometimes cause errors in unrelated kernel 530 areas and thus might be causing the issue you face. You therefore have to 531 prevent those modules from loading when you want to report an issue to the 532 Linux kernel developers. Most of the time the easiest way to do that is: 533 temporarily uninstall such software including any modules they might have 534 installed. Afterwards reboot. 535 536 3. The kernel also taints itself when it's loading a module that resides in 537 the staging tree of the Linux kernel source. That's a special area for 538 code (mostly drivers) that does not yet fulfill the normal Linux kernel 539 quality standards. When you report an issue with such a module it's 540 obviously okay if the kernel is tainted; just make sure the module in 541 question is the only reason for the taint. If the issue happens in an 542 unrelated area reboot and temporarily block the module from being loaded 543 by specifying ``foo.blacklist=1`` as kernel parameter (replace 'foo' with 544 the name of the module in question). 545 546 547Document how to reproduce issue 548------------------------------- 549 550 *Write down coarsely how to reproduce the issue. If you deal with multiple 551 issues at once, create separate notes for each of them and make sure they 552 work independently on a freshly booted system. That's needed, as each issue 553 needs to get reported to the kernel developers separately, unless they are 554 strongly entangled.* 555 556If you deal with multiple issues at once, you'll have to report each of them 557separately, as they might be handled by different developers. Describing 558various issues in one report also makes it quite difficult for others to tear 559it apart. Hence, only combine issues in one report if they are very strongly 560entangled. 561 562Additionally, during the reporting process you will have to test if the issue 563happens with other kernel versions. Therefore, it will make your work easier if 564you know exactly how to reproduce an issue quickly on a freshly booted system. 565 566Note: it's often fruitless to report issues that only happened once, as they 567might be caused by a bit flip due to cosmic radiation. That's why you should 568try to rule that out by reproducing the issue before going further. Feel free 569to ignore this advice if you are experienced enough to tell a one-time error 570due to faulty hardware apart from a kernel issue that rarely happens and thus 571is hard to reproduce. 572 573 574Regression in stable or longterm kernel? 575---------------------------------------- 576 577 *If you are facing a regression within a stable or longterm version line 578 (say something broke when updating from 5.10.4 to 5.10.5), scroll down to 579 'Dealing with regressions within a stable and longterm kernel line'.* 580 581Regression within a stable and longterm kernel version line are something the 582Linux developers want to fix badly, as such issues are even more unwanted than 583regression in the main development branch, as they can quickly affect a lot of 584people. The developers thus want to learn about such issues as quickly as 585possible, hence there is a streamlined process to report them. Note, 586regressions with newer kernel version line (say something broke when switching 587from 5.9.15 to 5.10.5) do not qualify. 588 589 590Check where you need to report your issue 591----------------------------------------- 592 593 *Locate the driver or kernel subsystem that seems to be causing the issue. 594 Find out how and where its developers expect reports. Note: most of the 595 time this won't be bugzilla.kernel.org, as issues typically need to be sent 596 by mail to a maintainer and a public mailing list.* 597 598It's crucial to send your report to the right people, as the Linux kernel is a 599big project and most of its developers are only familiar with a small subset of 600it. Quite a few programmers for example only care for just one driver, for 601example one for a WiFi chip; its developer likely will only have small or no 602knowledge about the internals of remote or unrelated "subsystems", like the TCP 603stack, the PCIe/PCI subsystem, memory management or file systems. 604 605Problem is: the Linux kernel lacks a central bug tracker where you can simply 606file your issue and make it reach the developers that need to know about it. 607That's why you have to find the right place and way to report issues yourself. 608You can do that with the help of a script (see below), but it mainly targets 609kernel developers and experts. For everybody else the MAINTAINERS file is the 610better place. 611 612How to read the MAINTAINERS file 613~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 614To illustrate how to use the :ref:`MAINTAINERS <maintainers>` file, lets assume 615the WiFi in your Laptop suddenly misbehaves after updating the kernel. In that 616case it's likely an issue in the WiFi driver. Obviously it could also be some 617code it builds upon, but unless you suspect something like that stick to the 618driver. If it's really something else, the driver's developers will get the 619right people involved. 620 621Sadly, there is no way to check which code is driving a particular hardware 622component that is both universal and easy. 623 624In case of a problem with the WiFi driver you for example might want to look at 625the output of ``lspci -k``, as it lists devices on the PCI/PCIe bus and the 626kernel module driving it:: 627 628 [user@something ~]$ lspci -k 629 [...] 630 3a:00.0 Network controller: Qualcomm Atheros QCA6174 802.11ac Wireless Network Adapter (rev 32) 631 Subsystem: Bigfoot Networks, Inc. Device 1535 632 Kernel driver in use: ath10k_pci 633 Kernel modules: ath10k_pci 634 [...] 635 636But this approach won't work if your WiFi chip is connected over USB or some 637other internal bus. In those cases you might want to check your WiFi manager or 638the output of ``ip link``. Look for the name of the problematic network 639interface, which might be something like 'wlp58s0'. This name can be used like 640this to find the module driving it:: 641 642 [user@something ~]$ realpath --relative-to=/sys/module/ /sys/class/net/wlp58s0/device/driver/module 643 ath10k_pci 644 645In case tricks like these don't bring you any further, try to search the 646internet on how to narrow down the driver or subsystem in question. And if you 647are unsure which it is: just try your best guess, somebody will help you if you 648guessed poorly. 649 650Once you know the driver or subsystem, you want to search for it in the 651MAINTAINERS file. In the case of 'ath10k_pci' you won't find anything, as the 652name is too specific. Sometimes you will need to search on the net for help; 653but before doing so, try a somewhat shorted or modified name when searching the 654MAINTAINERS file, as then you might find something like this:: 655 656 QUALCOMM ATHEROS ATH10K WIRELESS DRIVER 657 Mail: A. Some Human <shuman@example.com> 658 Mailing list: ath10k@lists.infradead.org 659 Status: Supported 660 Web-page: https://wireless.wiki.kernel.org/en/users/Drivers/ath10k 661 SCM: git git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git 662 Files: drivers/net/wireless/ath/ath10k/ 663 664Note: the line description will be abbreviations, if you read the plain 665MAINTAINERS file found in the root of the Linux source tree. 'Mail:' for 666example will be 'M:', 'Mailing list:' will be 'L', and 'Status:' will be 'S:'. 667A section near the top of the file explains these and other abbreviations. 668 669First look at the line 'Status'. Ideally it should be 'Supported' or 670'Maintained'. If it states 'Obsolete' then you are using some outdated approach 671that was replaced by a newer solution you need to switch to. Sometimes the code 672only has someone who provides 'Odd Fixes' when feeling motivated. And with 673'Orphan' you are totally out of luck, as nobody takes care of the code anymore. 674That only leaves these options: arrange yourself to live with the issue, fix it 675yourself, or find a programmer somewhere willing to fix it. 676 677After checking the status, look for a line starting with 'bugs:': it will tell 678you where to find a subsystem specific bug tracker to file your issue. The 679example above does not have such a line. That is the case for most sections, as 680Linux kernel development is completely driven by mail. Very few subsystems use 681a bug tracker, and only some of those rely on bugzilla.kernel.org. 682 683In this and many other cases you thus have to look for lines starting with 684'Mail:' instead. Those mention the name and the email addresses for the 685maintainers of the particular code. Also look for a line starting with 'Mailing 686list:', which tells you the public mailing list where the code is developed. 687Your report later needs to go by mail to those addresses. Additionally, for all 688issue reports sent by email, make sure to add the Linux Kernel Mailing List 689(LKML) <linux-kernel@vger.kernel.org> to CC. Don't omit either of the mailing 690lists when sending your issue report by mail later! Maintainers are busy people 691and might leave some work for other developers on the subsystem specific list; 692and LKML is important to have one place where all issue reports can be found. 693 694 695Finding the maintainers with the help of a script 696~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 697 698For people that have the Linux sources at hand there is a second option to find 699the proper place to report: the script 'scripts/get_maintainer.pl' which tries 700to find all people to contact. It queries the MAINTAINERS file and needs to be 701called with a path to the source code in question. For drivers compiled as 702module if often can be found with a command like this:: 703 704 $ modinfo ath10k_pci | grep filename | sed 's!/lib/modules/.*/kernel/!!; s!filename:!!; s!\.ko\(\|\.xz\)!!' 705 drivers/net/wireless/ath/ath10k/ath10k_pci.ko 706 707Pass parts of this to the script:: 708 709 $ ./scripts/get_maintainer.pl -f drivers/net/wireless/ath/ath10k* 710 Some Human <shuman@example.com> (supporter:QUALCOMM ATHEROS ATH10K WIRELESS DRIVER) 711 Another S. Human <asomehuman@example.com> (maintainer:NETWORKING DRIVERS) 712 ath10k@lists.infradead.org (open list:QUALCOMM ATHEROS ATH10K WIRELESS DRIVER) 713 linux-wireless@vger.kernel.org (open list:NETWORKING DRIVERS (WIRELESS)) 714 netdev@vger.kernel.org (open list:NETWORKING DRIVERS) 715 linux-kernel@vger.kernel.org (open list) 716 717Don't sent your report to all of them. Send it to the maintainers, which the 718script calls "supporter:"; additionally CC the most specific mailing list for 719the code as well as the Linux Kernel Mailing List (LKML). In this case you thus 720would need to send the report to 'Some Human <shuman@example.com>' with 721'ath10k@lists.infradead.org' and 'linux-kernel@vger.kernel.org' in CC. 722 723Note: in case you cloned the Linux sources with git you might want to call 724``get_maintainer.pl`` a second time with ``--git``. The script then will look 725at the commit history to find which people recently worked on the code in 726question, as they might be able to help. But use these results with care, as it 727can easily send you in a wrong direction. That for example happens quickly in 728areas rarely changed (like old or unmaintained drivers): sometimes such code is 729modified during tree-wide cleanups by developers that do not care about the 730particular driver at all. 731 732 733Search for existing reports, second run 734--------------------------------------- 735 736 *Search the archives of the bug tracker or mailing list in question 737 thoroughly for reports that might match your issue. If you find anything, 738 join the discussion instead of sending a new report.* 739 740As mentioned earlier already: reporting an issue that someone else already 741brought forward is often a waste of time for everyone involved, especially you 742as the reporter. That's why you should search for existing report again, now 743that you know where they need to be reported to. If it's mailing list, you will 744often find its archives on `lore.kernel.org <https://lore.kernel.org/>`_. 745 746But some list are hosted in different places. That for example is the case for 747the ath10k WiFi driver used as example in the previous step. But you'll often 748find the archives for these lists easily on the net. Searching for 'archive 749ath10k@lists.infradead.org' for example will lead you to the `Info page for the 750ath10k mailing list <https://lists.infradead.org/mailman/listinfo/ath10k>`_, 751which at the top links to its 752`list archives <https://lists.infradead.org/pipermail/ath10k/>`_. Sadly this and 753quite a few other lists miss a way to search the archives. In those cases use a 754regular internet search engine and add something like 755'site:lists.infradead.org/pipermail/ath10k/' to your search terms, which limits 756the results to the archives at that URL. 757 758It's also wise to check the internet, LKML and maybe bugzilla.kernel.org again 759at this point. If your report needs to be filed in a bug tracker, you may want 760to check the mailing list archives for the subsystem as well, as someone might 761have reported it only there. 762 763For details how to search and what to do if you find matching reports see 764"Search for existing reports, first run" above. 765 766Do not hurry with this step of the reporting process: spending 30 to 60 minutes 767or even more time can save you and others quite a lot of time and trouble. 768 769 770Install a fresh kernel for testing 771---------------------------------- 772 773 *Unless you are already running the latest 'mainline' Linux kernel, better 774 go and install it for the reporting process. Testing and reporting with 775 the latest 'stable' Linux can be an acceptable alternative in some 776 situations; during the merge window that actually might be even the best 777 approach, but in that development phase it can be an even better idea to 778 suspend your efforts for a few days anyway. Whatever version you choose, 779 ideally use a 'vanilla' built. Ignoring these advices will dramatically 780 increase the risk your report will be rejected or ignored.* 781 782As mentioned in the detailed explanation for the first step already: Like most 783programmers, Linux kernel developers don't like to spend time dealing with 784reports for issues that don't even happen with the current code. It's just a 785waste everybody's time, especially yours. That's why it's in everybody's 786interest that you confirm the issue still exists with the latest upstream code 787before reporting it. You are free to ignore this advice, but as outlined 788earlier: doing so dramatically increases the risk that your issue report might 789get rejected or simply ignored. 790 791In the scope of the kernel "latest upstream" normally means: 792 793 * Install a mainline kernel; the latest stable kernel can be an option, but 794 most of the time is better avoided. Longterm kernels (sometimes called 'LTS 795 kernels') are unsuitable at this point of the process. The next subsection 796 explains all of this in more detail. 797 798 * The over next subsection describes way to obtain and install such a kernel. 799 It also outlines that using a pre-compiled kernel are fine, but better are 800 vanilla, which means: it was built using Linux sources taken straight `from 801 kernel.org <https://kernel.org/>`_ and not modified or enhanced in any way. 802 803Choosing the right version for testing 804~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 805 806Head over to `kernel.org <https://kernel.org/>`_ to find out which version you 807want to use for testing. Ignore the big yellow button that says 'Latest release' 808and look a little lower at the table. At its top you'll see a line starting with 809mainline, which most of the time will point to a pre-release with a version 810number like '5.8-rc2'. If that's the case, you'll want to use this mainline 811kernel for testing, as that where all fixes have to be applied first. Do not let 812that 'rc' scare you, these 'development kernels' are pretty reliable ��� and you 813made a backup, as you were instructed above, didn't you? 814 815In about two out of every nine to ten weeks, mainline might point you to a 816proper release with a version number like '5.7'. If that happens, consider 817suspending the reporting process until the first pre-release of the next 818version (5.8-rc1) shows up on kernel.org. That's because the Linux development 819cycle then is in its two-week long 'merge window'. The bulk of the changes and 820all intrusive ones get merged for the next release during this time. It's a bit 821more risky to use mainline during this period. Kernel developers are also often 822quite busy then and might have no spare time to deal with issue reports. It's 823also quite possible that one of the many changes applied during the merge 824window fixes the issue you face; that's why you soon would have to retest with 825a newer kernel version anyway, as outlined below in the section 'Duties after 826the report went out'. 827 828That's why it might make sense to wait till the merge window is over. But don't 829to that if you're dealing with something that shouldn't wait. In that case 830consider obtaining the latest mainline kernel via git (see below) or use the 831latest stable version offered on kernel.org. Using that is also acceptable in 832case mainline for some reason does currently not work for you. An in general: 833using it for reproducing the issue is also better than not reporting it issue 834at all. 835 836Better avoid using the latest stable kernel outside merge windows, as all fixes 837must be applied to mainline first. That's why checking the latest mainline 838kernel is so important: any issue you want to see fixed in older version lines 839needs to be fixed in mainline first before it can get backported, which can 840take a few days or weeks. Another reason: the fix you hope for might be too 841hard or risky for backporting; reporting the issue again hence is unlikely to 842change anything. 843 844These aspects are also why longterm kernels (sometimes called "LTS kernels") 845are unsuitable for this part of the reporting process: they are to distant from 846the current code. Hence go and test mainline first and follow the process 847further: if the issue doesn't occur with mainline it will guide you how to get 848it fixed in older version lines, if that's in the cards for the fix in question. 849 850How to obtain a fresh Linux kernel 851~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 852 853**Using a pre-compiled kernel**: This is often the quickest, easiest, and safest 854way for testing ��� especially is you are unfamiliar with the Linux kernel. The 855problem: most of those shipped by distributors or add-on repositories are build 856from modified Linux sources. They are thus not vanilla and therefore often 857unsuitable for testing and issue reporting: the changes might cause the issue 858you face or influence it somehow. 859 860But you are in luck if you are using a popular Linux distribution: for quite a 861few of them you'll find repositories on the net that contain packages with the 862latest mainline or stable Linux built as vanilla kernel. It's totally okay to 863use these, just make sure from the repository's description they are vanilla or 864at least close to it. Additionally ensure the packages contain the latest 865versions as offered on kernel.org. The packages are likely unsuitable if they 866are older than a week, as new mainline and stable kernels typically get released 867at least once a week. 868 869Please note that you might need to build your own kernel manually later: that's 870sometimes needed for debugging or testing fixes, as described later in this 871document. Also be aware that pre-compiled kernels might lack debug symbols that 872are needed to decode messages the kernel prints when a panic, Oops, warning, or 873BUG occurs; if you plan to decode those, you might be better off compiling a 874kernel yourself (see the end of this subsection and the section titled 'Decode 875failure messages' for details). 876 877**Using git**: Developers and experienced Linux users familiar with git are 878often best served by obtaining the latest Linux kernel sources straight from the 879`official development repository on kernel.org 880<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/>`_. 881Those are likely a bit ahead of the latest mainline pre-release. Don't worry 882about it: they are as reliable as a proper pre-release, unless the kernel's 883development cycle is currently in the middle of a merge window. But even then 884they are quite reliable. 885 886**Conventional**: People unfamiliar with git are often best served by 887downloading the sources as tarball from `kernel.org <https://kernel.org/>`_. 888 889How to actually build a kernel is not described here, as many websites explain 890the necessary steps already. If you are new to it, consider following one of 891those how-to's that suggest to use ``make localmodconfig``, as that tries to 892pick up the configuration of your current kernel and then tries to adjust it 893somewhat for your system. That does not make the resulting kernel any better, 894but quicker to compile. 895 896Note: If you are dealing with a panic, Oops, warning, or BUG from the kernel, 897please try to enable CONFIG_KALLSYMS when configuring your kernel. 898Additionally, enable CONFIG_DEBUG_KERNEL and CONFIG_DEBUG_INFO, too; the 899latter is the relevant one of those two, but can only be reached if you enable 900the former. Be aware CONFIG_DEBUG_INFO increases the storage space required to 901build a kernel by quite a bit. But that's worth it, as these options will allow 902you later to pinpoint the exact line of code that triggers your issue. The 903section 'Decode failure messages' below explains this in more detail. 904 905But keep in mind: Always keep a record of the issue encountered in case it is 906hard to reproduce. Sending an undecoded report is better than not reporting 907the issue at all. 908 909 910Check 'taint' flag 911------------------ 912 913 *Ensure the kernel you just installed does not 'taint' itself when 914 running.* 915 916As outlined above in more detail already: the kernel sets a 'taint' flag when 917something happens that can lead to follow-up errors that look totally 918unrelated. That's why you need to check if the kernel you just installed does 919not set this flag. And if it does, you in almost all the cases needs to 920eliminate the reason for it before you reporting issues that occur with it. See 921the section above for details how to do that. 922 923 924Reproduce issue with the fresh kernel 925------------------------------------- 926 927 *Reproduce the issue with the kernel you just installed. If it doesn't show 928 up there, scroll down to the instructions for issues only happening with 929 stable and longterm kernels.* 930 931Check if the issue occurs with the fresh Linux kernel version you just 932installed. If it was fixed there already, consider sticking with this version 933line and abandoning your plan to report the issue. But keep in mind that other 934users might still be plagued by it, as long as it's not fixed in either stable 935and longterm version from kernel.org (and thus vendor kernels derived from 936those). If you prefer to use one of those or just want to help their users, 937head over to the section "Details about reporting issues only occurring in 938older kernel version lines" below. 939 940 941Optimize description to reproduce issue 942--------------------------------------- 943 944 *Optimize your notes: try to find and write the most straightforward way to 945 reproduce your issue. Make sure the end result has all the important 946 details, and at the same time is easy to read and understand for others 947 that hear about it for the first time. And if you learned something in this 948 process, consider searching again for existing reports about the issue.* 949 950An unnecessarily complex report will make it hard for others to understand your 951report. Thus try to find a reproducer that's straight forward to describe and 952thus easy to understand in written form. Include all important details, but at 953the same time try to keep it as short as possible. 954 955In this in the previous steps you likely have learned a thing or two about the 956issue you face. Use this knowledge and search again for existing reports 957instead you can join. 958 959 960Decode failure messages 961----------------------- 962 963 *If your failure involves a 'panic', 'Oops', 'warning', or 'BUG', consider 964 decoding the kernel log to find the line of code that triggered the error.* 965 966When the kernel detects an internal problem, it will log some information about 967the executed code. This makes it possible to pinpoint the exact line in the 968source code that triggered the issue and shows how it was called. But that only 969works if you enabled CONFIG_DEBUG_INFO and CONFIG_KALLSYMS when configuring 970your kernel. If you did so, consider to decode the information from the 971kernel's log. That will make it a lot easier to understand what lead to the 972'panic', 'Oops', 'warning', or 'BUG', which increases the chances that someone 973can provide a fix. 974 975Decoding can be done with a script you find in the Linux source tree. If you 976are running a kernel you compiled yourself earlier, call it like this:: 977 978 [user@something ~]$ sudo dmesg | ./linux-5.10.5/scripts/decode_stacktrace.sh ./linux-5.10.5/vmlinux 979 980If you are running a packaged vanilla kernel, you will likely have to install 981the corresponding packages with debug symbols. Then call the script (which you 982might need to get from the Linux sources if your distro does not package it) 983like this:: 984 985 [user@something ~]$ sudo dmesg | ./linux-5.10.5/scripts/decode_stacktrace.sh \ 986 /usr/lib/debug/lib/modules/5.10.10-4.1.x86_64/vmlinux /usr/src/kernels/5.10.10-4.1.x86_64/ 987 988The script will work on log lines like the following, which show the address of 989the code the kernel was executing when the error occurred:: 990 991 [ 68.387301] RIP: 0010:test_module_init+0x5/0xffa [test_module] 992 993Once decoded, these lines will look like this:: 994 995 [ 68.387301] RIP: 0010:test_module_init (/home/username/linux-5.10.5/test-module/test-module.c:16) test_module 996 997In this case the executed code was built from the file 998'~/linux-5.10.5/test-module/test-module.c' and the error occurred by the 999instructions found in line '16'. 1000 1001The script will similarly decode the addresses mentioned in the section 1002starting with 'Call trace', which show the path to the function where the 1003problem occurred. Additionally, the script will show the assembler output for 1004the code section the kernel was executing. 1005 1006Note, if you can't get this to work, simply skip this step and mention the 1007reason for it in the report. If you're lucky, it might not be needed. And if it 1008is, someone might help you to get things going. Also be aware this is just one 1009of several ways to decode kernel stack traces. Sometimes different steps will 1010be required to retrieve the relevant details. Don't worry about that, if that's 1011needed in your case, developers will tell you what to do. 1012 1013 1014Special care for regressions 1015---------------------------- 1016 1017 *If your problem is a regression, try to narrow down when the issue was 1018 introduced as much as possible.* 1019 1020Linux lead developer Linus Torvalds insists that the Linux kernel never 1021worsens, that's why he deems regressions as unacceptable and wants to see them 1022fixed quickly. That's why changes that introduced a regression are often 1023promptly reverted if the issue they cause can't get solved quickly any other 1024way. Reporting a regression is thus a bit like playing a kind of trump card to 1025get something quickly fixed. But for that to happen the change that's causing 1026the regression needs to be known. Normally it's up to the reporter to track 1027down the culprit, as maintainers often won't have the time or setup at hand to 1028reproduce it themselves. 1029 1030To find the change there is a process called 'bisection' which the document 1031Documentation/admin-guide/bug-bisect.rst describes in detail. That process 1032will often require you to build about ten to twenty kernel images, trying to 1033reproduce the issue with each of them before building the next. Yes, that takes 1034some time, but don't worry, it works a lot quicker than most people assume. 1035Thanks to a 'binary search' this will lead you to the one commit in the source 1036code management system that's causing the regression. Once you find it, search 1037the net for the subject of the change, its commit id and the shortened commit id 1038(the first 12 characters of the commit id). This will lead you to existing 1039reports about it, if there are any. 1040 1041Note, a bisection needs a bit of know-how, which not everyone has, and quite a 1042bit of effort, which not everyone is willing to invest. Nevertheless, it's 1043highly recommended performing a bisection yourself. If you really can't or 1044don't want to go down that route at least find out which mainline kernel 1045introduced the regression. If something for example breaks when switching from 10465.5.15 to 5.8.4, then try at least all the mainline releases in that area (5.6, 10475.7 and 5.8) to check when it first showed up. Unless you're trying to find a 1048regression in a stable or longterm kernel, avoid testing versions which number 1049has three sections (5.6.12, 5.7.8), as that makes the outcome hard to 1050interpret, which might render your testing useless. Once you found the major 1051version which introduced the regression, feel free to move on in the reporting 1052process. But keep in mind: it depends on the issue at hand if the developers 1053will be able to help without knowing the culprit. Sometimes they might 1054recognize from the report want went wrong and can fix it; other times they will 1055be unable to help unless you perform a bisection. 1056 1057When dealing with regressions make sure the issue you face is really caused by 1058the kernel and not by something else, as outlined above already. 1059 1060In the whole process keep in mind: an issue only qualifies as regression if the 1061older and the newer kernel got built with a similar configuration. This can be 1062achieved by using ``make olddefconfig``, as explained in more detail by 1063Documentation/admin-guide/reporting-regressions.rst; that document also 1064provides a good deal of other information about regressions you might want to be 1065aware of. 1066 1067 1068Write and send the report 1069------------------------- 1070 1071 *Start to compile the report by writing a detailed description about the 1072 issue. Always mention a few things: the latest kernel version you installed 1073 for reproducing, the Linux Distribution used, and your notes on how to 1074 reproduce the issue. Ideally, make the kernel's build configuration 1075 (.config) and the output from ``dmesg`` available somewhere on the net and 1076 link to it. Include or upload all other information that might be relevant, 1077 like the output/screenshot of an Oops or the output from ``lspci``. Once 1078 you wrote this main part, insert a normal length paragraph on top of it 1079 outlining the issue and the impact quickly. On top of this add one sentence 1080 that briefly describes the problem and gets people to read on. Now give the 1081 thing a descriptive title or subject that yet again is shorter. Then you're 1082 ready to send or file the report like the MAINTAINERS file told you, unless 1083 you are dealing with one of those 'issues of high priority': they need 1084 special care which is explained in 'Special handling for high priority 1085 issues' below.* 1086 1087Now that you have prepared everything it's time to write your report. How to do 1088that is partly explained by the three documents linked to in the preface above. 1089That's why this text will only mention a few of the essentials as well as 1090things specific to the Linux kernel. 1091 1092There is one thing that fits both categories: the most crucial parts of your 1093report are the title/subject, the first sentence, and the first paragraph. 1094Developers often get quite a lot of mail. They thus often just take a few 1095seconds to skim a mail before deciding to move on or look closer. Thus: the 1096better the top section of your report, the higher are the chances that someone 1097will look into it and help you. And that is why you should ignore them for now 1098and write the detailed report first. ;-) 1099 1100Things each report should mention 1101~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1102 1103Describe in detail how your issue happens with the fresh vanilla kernel you 1104installed. Try to include the step-by-step instructions you wrote and optimized 1105earlier that outline how you and ideally others can reproduce the issue; in 1106those rare cases where that's impossible try to describe what you did to 1107trigger it. 1108 1109Also include all the relevant information others might need to understand the 1110issue and its environment. What's actually needed depends a lot on the issue, 1111but there are some things you should include always: 1112 1113 * the output from ``cat /proc/version``, which contains the Linux kernel 1114 version number and the compiler it was built with. 1115 1116 * the Linux distribution the machine is running (``hostnamectl | grep 1117 "Operating System"``) 1118 1119 * the architecture of the CPU and the operating system (``uname -mi``) 1120 1121 * if you are dealing with a regression and performed a bisection, mention the 1122 subject and the commit-id of the change that is causing it. 1123 1124In a lot of cases it's also wise to make two more things available to those 1125that read your report: 1126 1127 * the configuration used for building your Linux kernel (the '.config' file) 1128 1129 * the kernel's messages that you get from ``dmesg`` written to a file. Make 1130 sure that it starts with a line like 'Linux version 5.8-1 1131 (foobar@example.com) (gcc (GCC) 10.2.1, GNU ld version 2.34) #1 SMP Mon Aug 1132 3 14:54:37 UTC 2020' If it's missing, then important messages from the first 1133 boot phase already got discarded. In this case instead consider using 1134 ``journalctl -b 0 -k``; alternatively you can also reboot, reproduce the 1135 issue and call ``dmesg`` right afterwards. 1136 1137These two files are big, that's why it's a bad idea to put them directly into 1138your report. If you are filing the issue in a bug tracker then attach them to 1139the ticket. If you report the issue by mail do not attach them, as that makes 1140the mail too large; instead do one of these things: 1141 1142 * Upload the files somewhere public (your website, a public file paste 1143 service, a ticket created just for this purpose on `bugzilla.kernel.org 1144 <https://bugzilla.kernel.org/>`_, ...) and include a link to them in your 1145 report. Ideally use something where the files stay available for years, as 1146 they could be useful to someone many years from now; this for example can 1147 happen if five or ten years from now a developer works on some code that was 1148 changed just to fix your issue. 1149 1150 * Put the files aside and mention you will send them later in individual 1151 replies to your own mail. Just remember to actually do that once the report 1152 went out. ;-) 1153 1154Things that might be wise to provide 1155~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1156 1157Depending on the issue you might need to add more background data. Here are a 1158few suggestions what often is good to provide: 1159 1160 * If you are dealing with a 'warning', an 'OOPS' or a 'panic' from the kernel, 1161 include it. If you can't copy'n'paste it, try to capture a netconsole trace 1162 or at least take a picture of the screen. 1163 1164 * If the issue might be related to your computer hardware, mention what kind 1165 of system you use. If you for example have problems with your graphics card, 1166 mention its manufacturer, the card's model, and what chip is uses. If it's a 1167 laptop mention its name, but try to make sure it's meaningful. 'Dell XPS 13' 1168 for example is not, because it might be the one from 2012; that one looks 1169 not that different from the one sold today, but apart from that the two have 1170 nothing in common. Hence, in such cases add the exact model number, which 1171 for example are '9380' or '7390' for XPS 13 models introduced during 2019. 1172 Names like 'Lenovo Thinkpad T590' are also somewhat ambiguous: there are 1173 variants of this laptop with and without a dedicated graphics chip, so try 1174 to find the exact model name or specify the main components. 1175 1176 * Mention the relevant software in use. If you have problems with loading 1177 modules, you want to mention the versions of kmod, systemd, and udev in use. 1178 If one of the DRM drivers misbehaves, you want to state the versions of 1179 libdrm and Mesa; also specify your Wayland compositor or the X-Server and 1180 its driver. If you have a filesystem issue, mention the version of 1181 corresponding filesystem utilities (e2fsprogs, btrfs-progs, xfsprogs, ...). 1182 1183 * Gather additional information from the kernel that might be of interest. The 1184 output from ``lspci -nn`` will for example help others to identify what 1185 hardware you use. If you have a problem with hardware you even might want to 1186 make the output from ``sudo lspci -vvv`` available, as that provides 1187 insights how the components were configured. For some issues it might be 1188 good to include the contents of files like ``/proc/cpuinfo``, 1189 ``/proc/ioports``, ``/proc/iomem``, ``/proc/modules``, or 1190 ``/proc/scsi/scsi``. Some subsystem also offer tools to collect relevant 1191 information. One such tool is ``alsa-info.sh`` `which the audio/sound 1192 subsystem developers provide <https://www.alsa-project.org/wiki/AlsaInfo>`_. 1193 1194Those examples should give your some ideas of what data might be wise to 1195attach, but you have to think yourself what will be helpful for others to know. 1196Don't worry too much about forgetting something, as developers will ask for 1197additional details they need. But making everything important available from 1198the start increases the chance someone will take a closer look. 1199 1200 1201The important part: the head of your report 1202~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1203 1204Now that you have the detailed part of the report prepared let's get to the 1205most important section: the first few sentences. Thus go to the top, add 1206something like 'The detailed description:' before the part you just wrote and 1207insert two newlines at the top. Now write one normal length paragraph that 1208describes the issue roughly. Leave out all boring details and focus on the 1209crucial parts readers need to know to understand what this is all about; if you 1210think this bug affects a lot of users, mention this to get people interested. 1211 1212Once you did that insert two more lines at the top and write a one sentence 1213summary that explains quickly what the report is about. After that you have to 1214get even more abstract and write an even shorter subject/title for the report. 1215 1216Now that you have written this part take some time to optimize it, as it is the 1217most important parts of your report: a lot of people will only read this before 1218they decide if reading the rest is time well spent. 1219 1220Now send or file the report like the :ref:`MAINTAINERS <maintainers>` file told 1221you, unless it's one of those 'issues of high priority' outlined earlier: in 1222that case please read the next subsection first before sending the report on 1223its way. 1224 1225Special handling for high priority issues 1226~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1227 1228Reports for high priority issues need special handling. 1229 1230**Severe issues**: make sure the subject or ticket title as well as the first 1231paragraph makes the severeness obvious. 1232 1233**Regressions**: make the report's subject start with '[REGRESSION]'. 1234 1235In case you performed a successful bisection, use the title of the change that 1236introduced the regression as the second part of your subject. Make the report 1237also mention the commit id of the culprit. In case of an unsuccessful bisection, 1238make your report mention the latest tested version that's working fine (say 5.7) 1239and the oldest where the issue occurs (say 5.8-rc1). 1240 1241When sending the report by mail, CC the Linux regressions mailing list 1242(regressions@lists.linux.dev). In case the report needs to be filed to some web 1243tracker, proceed to do so. Once filed, forward the report by mail to the 1244regressions list; CC the maintainer and the mailing list for the subsystem in 1245question. Make sure to inline the forwarded report, hence do not attach it. 1246Also add a short note at the top where you mention the URL to the ticket. 1247 1248When mailing or forwarding the report, in case of a successful bisection add the 1249author of the culprit to the recipients; also CC everyone in the signed-off-by 1250chain, which you find at the end of its commit message. 1251 1252**Security issues**: for these issues your will have to evaluate if a 1253short-term risk to other users would arise if details were publicly disclosed. 1254If that's not the case simply proceed with reporting the issue as described. 1255For issues that bear such a risk you will need to adjust the reporting process 1256slightly: 1257 1258 * If the MAINTAINERS file instructed you to report the issue by mail, do not 1259 CC any public mailing lists. 1260 1261 * If you were supposed to file the issue in a bug tracker make sure to mark 1262 the ticket as 'private' or 'security issue'. If the bug tracker does not 1263 offer a way to keep reports private, forget about it and send your report as 1264 a private mail to the maintainers instead. 1265 1266In both cases make sure to also mail your report to the addresses the 1267MAINTAINERS file lists in the section 'security contact'. Ideally directly CC 1268them when sending the report by mail. If you filed it in a bug tracker, forward 1269the report's text to these addresses; but on top of it put a small note where 1270you mention that you filed it with a link to the ticket. 1271 1272See Documentation/process/security-bugs.rst for more information. 1273 1274 1275Duties after the report went out 1276-------------------------------- 1277 1278 *Wait for reactions and keep the thing rolling until you can accept the 1279 outcome in one way or the other. Thus react publicly and in a timely manner 1280 to any inquiries. Test proposed fixes. Do proactive testing: retest with at 1281 least every first release candidate (RC) of a new mainline version and 1282 report your results. Send friendly reminders if things stall. And try to 1283 help yourself, if you don't get any help or if it's unsatisfying.* 1284 1285If your report was good and you are really lucky then one of the developers 1286might immediately spot what's causing the issue; they then might write a patch 1287to fix it, test it, and send it straight for integration in mainline while 1288tagging it for later backport to stable and longterm kernels that need it. Then 1289all you need to do is reply with a 'Thank you very much' and switch to a version 1290with the fix once it gets released. 1291 1292But this ideal scenario rarely happens. That's why the job is only starting 1293once you got the report out. What you'll have to do depends on the situations, 1294but often it will be the things listed below. But before digging into the 1295details, here are a few important things you need to keep in mind for this part 1296of the process. 1297 1298 1299General advice for further interactions 1300~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1301 1302**Always reply in public**: When you filed the issue in a bug tracker, always 1303reply there and do not contact any of the developers privately about it. For 1304mailed reports always use the 'Reply-all' function when replying to any mails 1305you receive. That includes mails with any additional data you might want to add 1306to your report: go to your mail applications 'Sent' folder and use 'reply-all' 1307on your mail with the report. This approach will make sure the public mailing 1308list(s) and everyone else that gets involved over time stays in the loop; it 1309also keeps the mail thread intact, which among others is really important for 1310mailing lists to group all related mails together. 1311 1312There are just two situations where a comment in a bug tracker or a 'Reply-all' 1313is unsuitable: 1314 1315 * Someone tells you to send something privately. 1316 1317 * You were told to send something, but noticed it contains sensitive 1318 information that needs to be kept private. In that case it's okay to send it 1319 in private to the developer that asked for it. But note in the ticket or a 1320 mail that you did that, so everyone else knows you honored the request. 1321 1322**Do research before asking for clarifications or help**: In this part of the 1323process someone might tell you to do something that requires a skill you might 1324not have mastered yet. For example, you might be asked to use some test tools 1325you never have heard of yet; or you might be asked to apply a patch to the 1326Linux kernel sources to test if it helps. In some cases it will be fine sending 1327a reply asking for instructions how to do that. But before going that route try 1328to find the answer own your own by searching the internet; alternatively 1329consider asking in other places for advice. For example ask a friend or post 1330about it to a chatroom or forum you normally hang out. 1331 1332**Be patient**: If you are really lucky you might get a reply to your report 1333within a few hours. But most of the time it will take longer, as maintainers 1334are scattered around the globe and thus might be in a different time zone ��� one 1335where they already enjoy their night away from keyboard. 1336 1337In general, kernel developers will take one to five business days to respond to 1338reports. Sometimes it will take longer, as they might be busy with the merge 1339windows, other work, visiting developer conferences, or simply enjoying a long 1340summer holiday. 1341 1342The 'issues of high priority' (see above for an explanation) are an exception 1343here: maintainers should address them as soon as possible; that's why you 1344should wait a week at maximum (or just two days if it's something urgent) 1345before sending a friendly reminder. 1346 1347Sometimes the maintainer might not be responding in a timely manner; other 1348times there might be disagreements, for example if an issue qualifies as 1349regression or not. In such cases raise your concerns on the mailing list and 1350ask others for public or private replies how to move on. If that fails, it 1351might be appropriate to get a higher authority involved. In case of a WiFi 1352driver that would be the wireless maintainers; if there are no higher level 1353maintainers or all else fails, it might be one of those rare situations where 1354it's okay to get Linus Torvalds involved. 1355 1356**Proactive testing**: Every time the first pre-release (the 'rc1') of a new 1357mainline kernel version gets released, go and check if the issue is fixed there 1358or if anything of importance changed. Mention the outcome in the ticket or in a 1359mail you sent as reply to your report (make sure it has all those in the CC 1360that up to that point participated in the discussion). This will show your 1361commitment and that you are willing to help. It also tells developers if the 1362issue persists and makes sure they do not forget about it. A few other 1363occasional retests (for example with rc3, rc5 and the final) are also a good 1364idea, but only report your results if something relevant changed or if you are 1365writing something anyway. 1366 1367With all these general things off the table let's get into the details of how 1368to help to get issues resolved once they were reported. 1369 1370Inquires and testing request 1371~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1372 1373Here are your duties in case you got replies to your report: 1374 1375**Check who you deal with**: Most of the time it will be the maintainer or a 1376developer of the particular code area that will respond to your report. But as 1377issues are normally reported in public it could be anyone that's replying ��� 1378including people that want to help, but in the end might guide you totally off 1379track with their questions or requests. That rarely happens, but it's one of 1380many reasons why it's wise to quickly run an internet search to see who you're 1381interacting with. By doing this you also get aware if your report was heard by 1382the right people, as a reminder to the maintainer (see below) might be in order 1383later if discussion fades out without leading to a satisfying solution for the 1384issue. 1385 1386**Inquiries for data**: Often you will be asked to test something or provide 1387additional details. Try to provide the requested information soon, as you have 1388the attention of someone that might help and risk losing it the longer you 1389wait; that outcome is even likely if you do not provide the information within 1390a few business days. 1391 1392**Requests for testing**: When you are asked to test a diagnostic patch or a 1393possible fix, try to test it in timely manner, too. But do it properly and make 1394sure to not rush it: mixing things up can happen easily and can lead to a lot 1395of confusion for everyone involved. A common mistake for example is thinking a 1396proposed patch with a fix was applied, but in fact wasn't. Things like that 1397happen even to experienced testers occasionally, but they most of the time will 1398notice when the kernel with the fix behaves just as one without it. 1399 1400What to do when nothing of substance happens 1401~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1402 1403Some reports will not get any reaction from the responsible Linux kernel 1404developers; or a discussion around the issue evolved, but faded out with 1405nothing of substance coming out of it. 1406 1407In these cases wait two (better: three) weeks before sending a friendly 1408reminder: maybe the maintainer was just away from keyboard for a while when 1409your report arrived or had something more important to take care of. When 1410writing the reminder, kindly ask if anything else from your side is needed to 1411get the ball running somehow. If the report got out by mail, do that in the 1412first lines of a mail that is a reply to your initial mail (see above) which 1413includes a full quote of the original report below: that's on of those few 1414situations where such a 'TOFU' (Text Over, Fullquote Under) is the right 1415approach, as then all the recipients will have the details at hand immediately 1416in the proper order. 1417 1418After the reminder wait three more weeks for replies. If you still don't get a 1419proper reaction, you first should reconsider your approach. Did you maybe try 1420to reach out to the wrong people? Was the report maybe offensive or so 1421confusing that people decided to completely stay away from it? The best way to 1422rule out such factors: show the report to one or two people familiar with FLOSS 1423issue reporting and ask for their opinion. Also ask them for their advice how 1424to move forward. That might mean: prepare a better report and make those people 1425review it before you send it out. Such an approach is totally fine; just 1426mention that this is the second and improved report on the issue and include a 1427link to the first report. 1428 1429If the report was proper you can send a second reminder; in it ask for advice 1430why the report did not get any replies. A good moment for this second reminder 1431mail is shortly after the first pre-release (the 'rc1') of a new Linux kernel 1432version got published, as you should retest and provide a status update at that 1433point anyway (see above). 1434 1435If the second reminder again results in no reaction within a week, try to 1436contact a higher-level maintainer asking for advice: even busy maintainers by 1437then should at least have sent some kind of acknowledgment. 1438 1439Remember to prepare yourself for a disappointment: maintainers ideally should 1440react somehow to every issue report, but they are only obliged to fix those 1441'issues of high priority' outlined earlier. So don't be too devastating if you 1442get a reply along the lines of 'thanks for the report, I have more important 1443issues to deal with currently and won't have time to look into this for the 1444foreseeable future'. 1445 1446It's also possible that after some discussion in the bug tracker or on a list 1447nothing happens anymore and reminders don't help to motivate anyone to work out 1448a fix. Such situations can be devastating, but is within the cards when it 1449comes to Linux kernel development. This and several other reasons for not 1450getting help are explained in 'Why some issues won't get any reaction or remain 1451unfixed after being reported' near the end of this document. 1452 1453Don't get devastated if you don't find any help or if the issue in the end does 1454not get solved: the Linux kernel is FLOSS and thus you can still help yourself. 1455You for example could try to find others that are affected and team up with 1456them to get the issue resolved. Such a team could prepare a fresh report 1457together that mentions how many you are and why this is something that in your 1458option should get fixed. Maybe together you can also narrow down the root cause 1459or the change that introduced a regression, which often makes developing a fix 1460easier. And with a bit of luck there might be someone in the team that knows a 1461bit about programming and might be able to write a fix. 1462 1463 1464Reference for "Reporting regressions within a stable and longterm kernel line" 1465------------------------------------------------------------------------------ 1466 1467This subsection provides details for the steps you need to perform if you face 1468a regression within a stable and longterm kernel line. 1469 1470Make sure the particular version line still gets support 1471~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1472 1473 *Check if the kernel developers still maintain the Linux kernel version 1474 line you care about: go to the front page of kernel.org and make sure it 1475 mentions the latest release of the particular version line without an 1476 '[EOL]' tag.* 1477 1478Most kernel version lines only get supported for about three months, as 1479maintaining them longer is quite a lot of work. Hence, only one per year is 1480chosen and gets supported for at least two years (often six). That's why you 1481need to check if the kernel developers still support the version line you care 1482for. 1483 1484Note, if kernel.org lists two stable version lines on the front page, you 1485should consider switching to the newer one and forget about the older one: 1486support for it is likely to be abandoned soon. Then it will get a "end-of-life" 1487(EOL) stamp. Version lines that reached that point still get mentioned on the 1488kernel.org front page for a week or two, but are unsuitable for testing and 1489reporting. 1490 1491Search stable mailing list 1492~~~~~~~~~~~~~~~~~~~~~~~~~~ 1493 1494 *Check the archives of the Linux stable mailing list for existing reports.* 1495 1496Maybe the issue you face is already known and was fixed or is about to. Hence, 1497`search the archives of the Linux stable mailing list 1498<https://lore.kernel.org/stable/>`_ for reports about an issue like yours. If 1499you find any matches, consider joining the discussion, unless the fix is 1500already finished and scheduled to get applied soon. 1501 1502Reproduce issue with the newest release 1503~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1504 1505 *Install the latest release from the particular version line as a vanilla 1506 kernel. Ensure this kernel is not tainted and still shows the problem, as 1507 the issue might have already been fixed there. If you first noticed the 1508 problem with a vendor kernel, check a vanilla build of the last version 1509 known to work performs fine as well.* 1510 1511Before investing any more time in this process you want to check if the issue 1512was already fixed in the latest release of version line you're interested in. 1513This kernel needs to be vanilla and shouldn't be tainted before the issue 1514happens, as detailed outlined already above in the section "Install a fresh 1515kernel for testing". 1516 1517Did you first notice the regression with a vendor kernel? Then changes the 1518vendor applied might be interfering. You need to rule that out by performing 1519a recheck. Say something broke when you updated from 5.10.4-vendor.42 to 15205.10.5-vendor.43. Then after testing the latest 5.10 release as outlined in 1521the previous paragraph check if a vanilla build of Linux 5.10.4 works fine as 1522well. If things are broken there, the issue does not qualify as upstream 1523regression and you need switch back to the main step-by-step guide to report 1524the issue. 1525 1526Report the regression 1527~~~~~~~~~~~~~~~~~~~~~ 1528 1529 *Send a short problem report to the Linux stable mailing list 1530 (stable@vger.kernel.org) and CC the Linux regressions mailing list 1531 (regressions@lists.linux.dev); if you suspect the cause in a particular 1532 subsystem, CC its maintainer and its mailing list. Roughly describe the 1533 issue and ideally explain how to reproduce it. Mention the first version 1534 that shows the problem and the last version that's working fine. Then 1535 wait for further instructions.* 1536 1537When reporting a regression that happens within a stable or longterm kernel 1538line (say when updating from 5.10.4 to 5.10.5) a brief report is enough for 1539the start to get the issue reported quickly. Hence a rough description to the 1540stable and regressions mailing list is all it takes; but in case you suspect 1541the cause in a particular subsystem, CC its maintainers and its mailing list 1542as well, because that will speed things up. 1543 1544And note, it helps developers a great deal if you can specify the exact version 1545that introduced the problem. Hence if possible within a reasonable time frame, 1546try to find that version using vanilla kernels. Lets assume something broke when 1547your distributor released a update from Linux kernel 5.10.5 to 5.10.8. Then as 1548instructed above go and check the latest kernel from that version line, say 15495.10.9. If it shows the problem, try a vanilla 5.10.5 to ensure that no patches 1550the distributor applied interfere. If the issue doesn't manifest itself there, 1551try 5.10.7 and then (depending on the outcome) 5.10.8 or 5.10.6 to find the 1552first version where things broke. Mention it in the report and state that 5.10.9 1553is still broken. 1554 1555What the previous paragraph outlines is basically a rough manual 'bisection'. 1556Once your report is out your might get asked to do a proper one, as it allows to 1557pinpoint the exact change that causes the issue (which then can easily get 1558reverted to fix the issue quickly). Hence consider to do a proper bisection 1559right away if time permits. See the section 'Special care for regressions' and 1560the document Documentation/admin-guide/bug-bisect.rst for details how to 1561perform one. In case of a successful bisection add the author of the culprit to 1562the recipients; also CC everyone in the signed-off-by chain, which you find at 1563the end of its commit message. 1564 1565 1566Reference for "Reporting issues only occurring in older kernel version lines" 1567----------------------------------------------------------------------------- 1568 1569This section provides details for the steps you need to take if you could not 1570reproduce your issue with a mainline kernel, but want to see it fixed in older 1571version lines (aka stable and longterm kernels). 1572 1573Some fixes are too complex 1574~~~~~~~~~~~~~~~~~~~~~~~~~~ 1575 1576 *Prepare yourself for the possibility that going through the next few steps 1577 might not get the issue solved in older releases: the fix might be too big 1578 or risky to get backported there.* 1579 1580Even small and seemingly obvious code-changes sometimes introduce new and 1581totally unexpected problems. The maintainers of the stable and longterm kernels 1582are very aware of that and thus only apply changes to these kernels that are 1583within rules outlined in Documentation/process/stable-kernel-rules.rst. 1584 1585Complex or risky changes for example do not qualify and thus only get applied 1586to mainline. Other fixes are easy to get backported to the newest stable and 1587longterm kernels, but too risky to integrate into older ones. So be aware the 1588fix you are hoping for might be one of those that won't be backported to the 1589version line your care about. In that case you'll have no other choice then to 1590live with the issue or switch to a newer Linux version, unless you want to 1591patch the fix into your kernels yourself. 1592 1593Common preparations 1594~~~~~~~~~~~~~~~~~~~ 1595 1596 *Perform the first three steps in the section "Reporting issues only 1597 occurring in older kernel version lines" above.* 1598 1599You need to carry out a few steps already described in another section of this 1600guide. Those steps will let you: 1601 1602 * Check if the kernel developers still maintain the Linux kernel version line 1603 you care about. 1604 1605 * Search the Linux stable mailing list for exiting reports. 1606 1607 * Check with the latest release. 1608 1609 1610Check code history and search for existing discussions 1611~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1612 1613 *Search the Linux kernel version control system for the change that fixed 1614 the issue in mainline, as its commit message might tell you if the fix is 1615 scheduled for backporting already. If you don't find anything that way, 1616 search the appropriate mailing lists for posts that discuss such an issue 1617 or peer-review possible fixes; then check the discussions if the fix was 1618 deemed unsuitable for backporting. If backporting was not considered at 1619 all, join the newest discussion, asking if it's in the cards.* 1620 1621In a lot of cases the issue you deal with will have happened with mainline, but 1622got fixed there. The commit that fixed it would need to get backported as well 1623to get the issue solved. That's why you want to search for it or any 1624discussions abound it. 1625 1626 * First try to find the fix in the Git repository that holds the Linux kernel 1627 sources. You can do this with the web interfaces `on kernel.org 1628 <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/>`_ 1629 or its mirror `on GitHub <https://github.com/torvalds/linux>`_; if you have 1630 a local clone you alternatively can search on the command line with ``git 1631 log --grep=<pattern>``. 1632 1633 If you find the fix, look if the commit message near the end contains a 1634 'stable tag' that looks like this: 1635 1636 Cc: <stable@vger.kernel.org> # 5.4+ 1637 1638 If that's case the developer marked the fix safe for backporting to version 1639 line 5.4 and later. Most of the time it's getting applied there within two 1640 weeks, but sometimes it takes a bit longer. 1641 1642 * If the commit doesn't tell you anything or if you can't find the fix, look 1643 again for discussions about the issue. Search the net with your favorite 1644 internet search engine as well as the archives for the `Linux kernel 1645 developers mailing list <https://lore.kernel.org/lkml/>`_. Also read the 1646 section `Locate kernel area that causes the issue` above and follow the 1647 instructions to find the subsystem in question: its bug tracker or mailing 1648 list archive might have the answer you are looking for. 1649 1650 * If you see a proposed fix, search for it in the version control system as 1651 outlined above, as the commit might tell you if a backport can be expected. 1652 1653 * Check the discussions for any indicators the fix might be too risky to get 1654 backported to the version line you care about. If that's the case you have 1655 to live with the issue or switch to the kernel version line where the fix 1656 got applied. 1657 1658 * If the fix doesn't contain a stable tag and backporting was not discussed, 1659 join the discussion: mention the version where you face the issue and that 1660 you would like to see it fixed, if suitable. 1661 1662 1663Ask for advice 1664~~~~~~~~~~~~~~ 1665 1666 *One of the former steps should lead to a solution. If that doesn't work 1667 out, ask the maintainers for the subsystem that seems to be causing the 1668 issue for advice; CC the mailing list for the particular subsystem as well 1669 as the stable mailing list.* 1670 1671If the previous three steps didn't get you closer to a solution there is only 1672one option left: ask for advice. Do that in a mail you sent to the maintainers 1673for the subsystem where the issue seems to have its roots; CC the mailing list 1674for the subsystem as well as the stable mailing list (stable@vger.kernel.org). 1675 1676 1677Why some issues won't get any reaction or remain unfixed after being reported 1678============================================================================= 1679 1680When reporting a problem to the Linux developers, be aware only 'issues of high 1681priority' (regressions, security issues, severe problems) are definitely going 1682to get resolved. The maintainers or if all else fails Linus Torvalds himself 1683will make sure of that. They and the other kernel developers will fix a lot of 1684other issues as well. But be aware that sometimes they can't or won't help; and 1685sometimes there isn't even anyone to send a report to. 1686 1687This is best explained with kernel developers that contribute to the Linux 1688kernel in their spare time. Quite a few of the drivers in the kernel were 1689written by such programmers, often because they simply wanted to make their 1690hardware usable on their favorite operating system. 1691 1692These programmers most of the time will happily fix problems other people 1693report. But nobody can force them to do, as they are contributing voluntarily. 1694 1695Then there are situations where such developers really want to fix an issue, 1696but can't: sometimes they lack hardware programming documentation to do so. 1697This often happens when the publicly available docs are superficial or the 1698driver was written with the help of reverse engineering. 1699 1700Sooner or later spare time developers will also stop caring for the driver. 1701Maybe their test hardware broke, got replaced by something more fancy, or is so 1702old that it's something you don't find much outside of computer museums 1703anymore. Sometimes developer stops caring for their code and Linux at all, as 1704something different in their life became way more important. In some cases 1705nobody is willing to take over the job as maintainer ��� and nobody can be forced 1706to, as contributing to the Linux kernel is done on a voluntary basis. Abandoned 1707drivers nevertheless remain in the kernel: they are still useful for people and 1708removing would be a regression. 1709 1710The situation is not that different with developers that are paid for their 1711work on the Linux kernel. Those contribute most changes these days. But their 1712employers sooner or later also stop caring for their code or make its 1713programmer focus on other things. Hardware vendors for example earn their money 1714mainly by selling new hardware; quite a few of them hence are not investing 1715much time and energy in maintaining a Linux kernel driver for something they 1716stopped selling years ago. Enterprise Linux distributors often care for a 1717longer time period, but in new versions often leave support for old and rare 1718hardware aside to limit the scope. Often spare time contributors take over once 1719a company orphans some code, but as mentioned above: sooner or later they will 1720leave the code behind, too. 1721 1722Priorities are another reason why some issues are not fixed, as maintainers 1723quite often are forced to set those, as time to work on Linux is limited. 1724That's true for spare time or the time employers grant their developers to 1725spend on maintenance work on the upstream kernel. Sometimes maintainers also 1726get overwhelmed with reports, even if a driver is working nearly perfectly. To 1727not get completely stuck, the programmer thus might have no other choice than 1728to prioritize issue reports and reject some of them. 1729 1730But don't worry too much about all of this, a lot of drivers have active 1731maintainers who are quite interested in fixing as many issues as possible. 1732 1733 1734Closing words 1735============= 1736 1737Compared with other Free/Libre & Open Source Software it's hard to report 1738issues to the Linux kernel developers: the length and complexity of this 1739document and the implications between the lines illustrate that. But that's how 1740it is for now. The main author of this text hopes documenting the state of the 1741art will lay some groundwork to improve the situation over time. 1742 1743 1744.. 1745 end-of-content 1746.. 1747 This document is maintained by Thorsten Leemhuis <linux@leemhuis.info>. If 1748 you spot a typo or small mistake, feel free to let him know directly and 1749 he'll fix it. You are free to do the same in a mostly informal way if you 1750 want to contribute changes to the text, but for copyright reasons please CC 1751 linux-doc@vger.kernel.org and "sign-off" your contribution as 1752 Documentation/process/submitting-patches.rst outlines in the section "Sign 1753 your work - the Developer's Certificate of Origin". 1754.. 1755 This text is available under GPL-2.0+ or CC-BY-4.0, as stated at the top 1756 of the file. If you want to distribute this text under CC-BY-4.0 only, 1757 please use "The Linux kernel developers" for author attribution and link 1758 this as source: 1759 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/admin-guide/reporting-issues.rst 1760.. 1761 Note: Only the content of this RST file as found in the Linux kernel sources 1762 is available under CC-BY-4.0, as versions of this text that were processed 1763 (for example by the kernel's build system) might contain content taken from 1764 files which use a more restrictive license. 1765