1.\" 2.\" Copyright (C) 2002 Chad David <davidc@acns.ab.ca>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as 9.\" the first lines of this file unmodified other than the possible 10.\" addition of one or more copyright notices. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice(s), this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 16.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 17.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 18.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 19.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 22.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 25.\" DAMAGE. 26.\"
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27.\" $FreeBSD: head/share/man/man9/lock.9 177697 2008-03-28 21:30:37Z brueffer $
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27.\" $FreeBSD: head/share/man/man9/lock.9 177962 2008-04-06 21:22:12Z attilio $ |
28.\"
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29.Dd March 28, 2008
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29.Dd April 6, 2008 |
30.Dt LOCK 9 31.Os 32.Sh NAME 33.Nm lockinit , 34.Nm lockdestroy , 35.Nm lockmgr , 36.Nm lockmgr_args ,
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37.Nm lockmgr_args_rw , |
38.Nm lockmgr_disown , 39.Nm lockmgr_printinfo , 40.Nm lockmgr_recursed ,
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41.Nm lockmgr_rw , |
42.Nm lockmgr_waiters , 43.Nm lockstatus , 44.Nm lockmgr_assert 45.Nd "lockmgr family of functions" 46.Sh SYNOPSIS 47.In sys/types.h 48.In sys/lock.h 49.In sys/lockmgr.h 50.Ft void 51.Fn lockinit "struct lock *lkp" "int prio" "const char *wmesg" "int timo" "int flags" 52.Ft void 53.Fn lockdestroy "struct lock *lkp" 54.Ft int
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53.Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *interlkp"
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55.Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *ilk" |
56.Ft int
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55.Fn lockmgr_args "struct lock *lkp" "u_int flags" "struct mtx *interlkp" "const char *wmesg" "int prio" "int timo"
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57.Fn lockmgr_args "struct lock *lkp" "u_int flags" "struct mtx *ilk" "const char *wmesg" "int prio" "int timo" 58.Ft int 59.Fn lockmgr_args_rw "struct lock *lkp" "u_int flags" "struct rwlock *ilk" "const char *wmesg" "int prio" "int timo" |
60.Ft void 61.Fn lockmgr_disown "struct lock *lkp" 62.Ft void 63.Fn lockmgr_printinfo "struct lock *lkp" 64.Ft int 65.Fn lockmgr_recursed "struct lock *lkp" 66.Ft int
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67.Fn lockmgr_rw "struct lock *lkp" "u_int flags" "struct rwlock *ilk" 68.Ft int |
69.Fn lockmgr_waiters "struct lock *lkp" 70.Ft int 71.Fn lockstatus "struct lock *lkp" 72.Pp 73.Cd "options INVARIANTS" 74.Cd "options INVARIANT_SUPPORT" 75.Ft void 76.Fn lockmgr_assert "struct lock *lkp" "int what" 77.Sh DESCRIPTION 78The 79.Fn lockinit 80function is used to initialize a lock. 81It must be called before any operation can be performed on a lock. 82Its arguments are: 83.Bl -tag -width ".Fa wmesg" 84.It Fa lkp 85A pointer to the lock to initialize. 86.It Fa prio 87The priority passed to 88.Xr sleep 9 . 89.It Fa wmesg 90The lock message. 91This is used for both debugging output and 92.Xr sleep 9 . 93.It Fa timo 94The timeout value passed to 95.Xr sleep 9 . 96.It Fa flags 97The flags the lock is to be initialized with: 98.Bl -tag -width ".Dv LK_CANRECURSE" 99.It Dv LK_CANRECURSE 100Allow recursive exclusive locks. 101.It Dv LK_NOPROFILE 102Disable lock profiling for this lock. 103.It Dv LK_NOSHARE 104Allow exclusive locks only. 105.It Dv LK_NOWITNESS 106Instruct 107.Xr witness 4 108to ignore this lock. 109.It Dv LK_NODUP 110.Xr witness 4 111should log messages about duplicate locks being acquired. 112.It Dv LK_QUIET 113Disable 114.Xr ktr 4 115logging for this lock. 116.It Dv LK_TIMELOCK 117Use 118.Fa timo 119during a sleep; otherwise, 0 is used. 120.El 121.El 122.Pp 123The 124.Fn lockdestroy 125function is used to destroy a lock, and while it is called in a number of 126places in the kernel, it currently does nothing. 127.Pp 128The 129.Fn lockmgr
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124function handles general locking functionality within the kernel, including
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130and 131.Fn lockmgr_rw 132functions handle general locking functionality within the kernel, including |
133support for shared and exclusive locks, and recursion. 134.Fn lockmgr
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127is also able to upgrade and downgrade locks.
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135and 136.Fn lockmgr_rw 137are also able to upgrade and downgrade locks. |
138.Pp
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129Its arguments are:
130.Bl -tag -width ".Fa interlkp"
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139Their arguments are: 140.Bl -tag -width ".Fa flags" |
141.It Fa lkp 142A pointer to the lock to manipulate. 143.It Fa flags 144Flags indicating what action is to be taken. 145.Bl -tag -width ".Dv LK_CANRECURSE" 146.It Dv LK_SHARED 147Acquire a shared lock. 148If an exclusive lock is currently held, it will be downgraded. 149.It Dv LK_EXCLUSIVE 150Acquire an exclusive lock. 151If an exclusive lock is already held, and 152.Dv LK_CANRECURSE 153is not set, the system will 154.Xr panic 9 . 155.It Dv LK_DOWNGRADE 156Downgrade exclusive lock to a shared lock. 157Downgrading a shared lock is not permitted. 158If an exclusive lock has been recursed, all references will be downgraded. 159.It Dv LK_UPGRADE 160Upgrade a shared lock to an exclusive lock. 161If this call fails, the shared lock is lost. 162During the upgrade, the shared lock could 163be temporarily dropped. 164Attempts to upgrade an exclusive lock will cause a 165.Xr panic 9 . 166.It Dv LK_RELEASE 167Release the lock. 168Releasing a lock that is not held can cause a 169.Xr panic 9 . 170.It Dv LK_DRAIN 171Wait for all activity on the lock to end, then mark it decommissioned. 172This is used before freeing a lock that is part of a piece of memory that is 173about to be freed. 174(As documented in 175.In sys/lockmgr.h . ) 176.It Dv LK_SLEEPFAIL 177Fail if operation has slept. 178.It Dv LK_NOWAIT 179Do not allow the call to sleep. 180This can be used to test the lock. 181.It Dv LK_CANRECURSE 182Allow recursion on an exclusive lock. 183For every lock there must be a release. 184.It Dv LK_INTERLOCK 185Unlock the interlock (which should be locked already). 186.El
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177.It Fa interlkp
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187.It Fa ilk |
188An interlock mutex for controlling group access to the lock. 189If 190.Dv LK_INTERLOCK 191is specified, 192.Fn lockmgr
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183assumes
184.Fa interlkp
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193and 194.Fn lockmgr_rw 195assume 196.Fa ilk |
197is currently owned and not recursed, and will return it unlocked. 198See 199.Xr mtx_assert 9 . 200.El 201.Pp 202The 203.Fn lockmgr_args
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192function works like
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204and 205.Fn lockmgr_args_rw 206function work like |
207.Fn lockmgr
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208and 209.Fn lockmgr_rw |
210but accepting a 211.Fa wmesg , 212.Fa timo 213and 214.Fa prio 215on a per-instance basis. 216The specified values will override the default 217ones, but this can still be used passing, respectively, 218.Dv LK_WMESG_DEFAULT , 219.Dv LK_PRIO_DEFAULT 220and 221.Dv LK_TIMO_DEFAULT . 222.Pp 223The 224.Fn lockmgr_disown 225function switches the owner from the current thread to be 226.Dv LK_KERNPROC, 227if the lock is already held. 228.Pp 229The 230.Fn lockmgr_printinfo 231function prints debugging information about the lock. 232It is used primarily by 233.Xr VOP_PRINT 9 234functions. 235.Pp 236The 237.Fn lockmgr_recursed 238function returns true if the lock is recursed, 0 239otherwise. 240.Pp 241The 242.Fn lockmgr_waiters 243function returns true if the lock has waiters, 0 otherwise. 244.Pp 245The 246.Fn lockstatus 247function returns the status of the lock in relation to the current thread. 248.Pp 249When compiled with 250.Cd "options INVARIANTS" 251and 252.Cd "options INVARIANT_SUPPORT" , 253the 254.Fn lockmgr_assert 255function tests 256.Fa lkp 257for the assertions specified in 258.Fa what , 259and panics if they are not met. 260One of the following assertions must be specified: 261.Bl -tag -width ".Dv KA_UNLOCKED" 262.It Dv KA_LOCKED 263Assert that the current thread has either a shared or an exclusive lock on the 264.Vt lkp 265lock pointed to by the first argument. 266.It Dv KA_SLOCKED 267Assert that the current thread has a shared lock on the 268.Vt lkp 269lock pointed to by the first argument. 270.It Dv KA_XLOCKED 271Assert that the current thread has an exclusive lock on the 272.Vt lkp 273lock pointed to by the first argument. 274.It Dv KA_UNLOCKED 275Assert that the current thread has no lock on the 276.Vt lkp 277lock pointed to by the first argument. 278.It Dv KA_HELD 279Assert that an unspecified thread has a lock on the 280.Vt lkp 281lock pointed to by the first argument. 282.It Dv KA_UNHELD 283Assert that no thread has a lock on the 284.Vt lkp 285lock pointed to by the first argument. 286.El 287.Pp 288In addition, one of the following optional assertions can be used with 289either an 290.Dv KA_LOCKED , 291.Dv KA_SLOCKED , 292or 293.Dv KA_XLOCKED 294assertion: 295.Bl -tag -width ".Dv KA_NOTRECURSED" 296.It Dv KA_RECURSED 297Assert that the current thread has a recursed lock on 298.Fa lkp . 299.It Dv KA_NOTRECURSED 300Assert that the current thread does not have a recursed lock on 301.Fa lkp . 302.El 303.Pp 304Note that 305.Dv KA_HELD 306and 307.Dv KA_UNHELD 308usage is highly discouraged. 309They are intended to cater a bad behaviour 310introduced by buffer cache lock handling. 311They will hopefully be 312made useless by revisiting such locks. 313.Sh RETURN VALUES 314The 315.Fn lockmgr
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300function returns 0 on success and non-zero on failure.
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316and 317.Fn lockmgr_rw 318functions return 0 on success and non-zero on failure. |
319.Pp 320The 321.Fn lockstatus 322function returns: 323.Bl -tag -width ".Dv LK_EXCLUSIVE" 324.It Dv LK_EXCLUSIVE 325An exclusive lock is held by the current thread. 326.It Dv LK_EXCLOTHER 327An exclusive lock is held by someone other than the current thread. 328.It Dv LK_SHARED 329A shared lock is held. 330.It Li 0 331The lock is not held by anyone. 332.El 333.Sh ERRORS 334.Fn lockmgr
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317fails if:
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335and 336.Fn lockmgr_rw 337fail if: |
338.Bl -tag -width Er 339.It Bq Er EBUSY 340.Dv LK_FORCEUPGRADE 341was requested and another thread had already requested a lock upgrade. 342.It Bq Er EBUSY 343.Dv LK_NOWAIT 344was set, and a sleep would have been required. 345.It Bq Er ENOLCK 346.Dv LK_SLEEPFAIL 347was set and 348.Fn lockmgr
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349or 350.Fn lockmgr_rw |
351did sleep. 352.It Bq Er EINTR 353.Dv PCATCH 354was set in the lock priority, and a signal was delivered during a sleep. 355Note the 356.Er ERESTART 357error below. 358.It Bq Er ERESTART 359.Dv PCATCH 360was set in the lock priority, a signal was delivered during a sleep, 361and the system call is to be restarted. 362.It Bq Er EWOULDBLOCK 363a non-zero timeout was given, and the timeout expired. 364.El 365.Sh LOCKS 366If 367.Dv LK_INTERLOCK 368is passed in the 369.Fa flags 370argument to
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349.Fn lockmgr ,
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371.Fn lockmgr 372or 373.Fn lockmgr_rw , |
374the
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351.Fa interlkp
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375.Fa ilk |
376must be held prior to calling
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353.Fn lockmgr ,
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377.Fn lockmgr 378or 379.Fn lockmgr_rw , |
380and will be returned unlocked. 381.Pp 382Upgrade attempts that fail result in the loss of the lock that 383is currently held. 384Also, it is invalid to upgrade an 385exclusive lock, and a 386.Xr panic 9 387will be the result of trying. 388.Sh SEE ALSO 389.Xr condvar 9 , 390.Xr locking 9 , 391.Xr mutex 9 , 392.Xr rwlock 9 , 393.Xr sleep 9 , 394.Xr sx 9 , 395.Xr mtx_assert 9 , 396.Xr panic 9 , 397.Xr VOP_PRINT 9 398.Sh AUTHORS 399This manual page was written by 400.An Chad David Aq davidc@acns.ab.ca .
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