linux_rcu.c revision 359958
1/*- 2 * Copyright (c) 2016 Matthew Macy (mmacy@mattmacy.io) 3 * Copyright (c) 2017-2020 Hans Petter Selasky (hselasky@freebsd.org) 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice unmodified, this list of conditions, and the following 11 * disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28#include <sys/cdefs.h> 29__FBSDID("$FreeBSD: stable/11/sys/compat/linuxkpi/common/src/linux_rcu.c 359958 2020-04-15 05:02:49Z hselasky $"); 30 31#include <sys/types.h> 32#include <sys/systm.h> 33#include <sys/malloc.h> 34#include <sys/kernel.h> 35#include <sys/lock.h> 36#include <sys/mutex.h> 37#include <sys/proc.h> 38#include <sys/sched.h> 39#include <sys/smp.h> 40#include <sys/queue.h> 41#include <sys/taskqueue.h> 42#include <sys/kdb.h> 43 44#include <ck_epoch.h> 45 46#include <linux/rcupdate.h> 47#include <linux/srcu.h> 48#include <linux/slab.h> 49#include <linux/kernel.h> 50#include <linux/compat.h> 51 52/* 53 * By defining CONFIG_NO_RCU_SKIP LinuxKPI RCU locks and asserts will 54 * not be skipped during panic(). 55 */ 56#ifdef CONFIG_NO_RCU_SKIP 57#define RCU_SKIP(void) 0 58#else 59#define RCU_SKIP(void) unlikely(SCHEDULER_STOPPED() || kdb_active) 60#endif 61 62struct callback_head { 63 STAILQ_ENTRY(callback_head) entry; 64 rcu_callback_t func; 65}; 66 67struct linux_epoch_head { 68 STAILQ_HEAD(, callback_head) cb_head; 69 struct mtx lock; 70 struct task task; 71} __aligned(CACHE_LINE_SIZE); 72 73struct linux_epoch_record { 74 ck_epoch_record_t epoch_record; 75 TAILQ_HEAD(, task_struct) ts_head; 76 int cpuid; 77} __aligned(CACHE_LINE_SIZE); 78 79/* 80 * Verify that "struct rcu_head" is big enough to hold "struct 81 * callback_head". This has been done to avoid having to add special 82 * compile flags for including ck_epoch.h to all clients of the 83 * LinuxKPI. 84 */ 85CTASSERT(sizeof(struct rcu_head) == sizeof(struct callback_head)); 86 87/* 88 * Verify that "epoch_record" is at beginning of "struct 89 * linux_epoch_record": 90 */ 91CTASSERT(offsetof(struct linux_epoch_record, epoch_record) == 0); 92 93static ck_epoch_t linux_epoch[RCU_TYPE_MAX]; 94static struct linux_epoch_head linux_epoch_head[RCU_TYPE_MAX]; 95static DPCPU_DEFINE(struct linux_epoch_record, linux_epoch_record[RCU_TYPE_MAX]); 96 97static void linux_rcu_cleaner_func(void *, int); 98 99static void 100linux_rcu_runtime_init(void *arg __unused) 101{ 102 struct linux_epoch_head *head; 103 int i; 104 int j; 105 106 for (j = 0; j != RCU_TYPE_MAX; j++) { 107 ck_epoch_init(&linux_epoch[j]); 108 109 head = &linux_epoch_head[j]; 110 111 mtx_init(&head->lock, "LRCU-HEAD", NULL, MTX_DEF); 112 TASK_INIT(&head->task, 0, linux_rcu_cleaner_func, head); 113 STAILQ_INIT(&head->cb_head); 114 115 CPU_FOREACH(i) { 116 struct linux_epoch_record *record; 117 118 record = &DPCPU_ID_GET(i, linux_epoch_record[j]); 119 120 record->cpuid = i; 121 ck_epoch_register(&linux_epoch[j], 122 &record->epoch_record, NULL); 123 TAILQ_INIT(&record->ts_head); 124 } 125 } 126} 127SYSINIT(linux_rcu_runtime, SI_SUB_CPU, SI_ORDER_ANY, linux_rcu_runtime_init, NULL); 128 129static void 130linux_rcu_runtime_uninit(void *arg __unused) 131{ 132 struct linux_epoch_head *head; 133 int j; 134 135 for (j = 0; j != RCU_TYPE_MAX; j++) { 136 head = &linux_epoch_head[j]; 137 138 mtx_destroy(&head->lock); 139 } 140} 141SYSUNINIT(linux_rcu_runtime, SI_SUB_LOCK, SI_ORDER_SECOND, linux_rcu_runtime_uninit, NULL); 142 143static void 144linux_rcu_cleaner_func(void *context, int pending __unused) 145{ 146 struct linux_epoch_head *head; 147 struct callback_head *rcu; 148 STAILQ_HEAD(, callback_head) tmp_head; 149 uintptr_t offset; 150 151 linux_set_current(curthread); 152 153 head = context; 154 155 /* move current callbacks into own queue */ 156 mtx_lock(&head->lock); 157 STAILQ_INIT(&tmp_head); 158 STAILQ_CONCAT(&tmp_head, &head->cb_head); 159 mtx_unlock(&head->lock); 160 161 /* synchronize */ 162 linux_synchronize_rcu(head - linux_epoch_head); 163 164 /* dispatch all callbacks, if any */ 165 while ((rcu = STAILQ_FIRST(&tmp_head)) != NULL) { 166 167 STAILQ_REMOVE_HEAD(&tmp_head, entry); 168 169 offset = (uintptr_t)rcu->func; 170 171 if (offset < LINUX_KFREE_RCU_OFFSET_MAX) 172 kfree((char *)rcu - offset); 173 else 174 rcu->func((struct rcu_head *)rcu); 175 } 176} 177 178void 179linux_rcu_read_lock(unsigned type) 180{ 181 struct linux_epoch_record *record; 182 struct task_struct *ts; 183 184 MPASS(type < RCU_TYPE_MAX); 185 186 if (RCU_SKIP()) 187 return; 188 189 /* 190 * Pin thread to current CPU so that the unlock code gets the 191 * same per-CPU epoch record: 192 */ 193 sched_pin(); 194 195 record = &DPCPU_GET(linux_epoch_record[type]); 196 ts = current; 197 198 /* 199 * Use a critical section to prevent recursion inside 200 * ck_epoch_begin(). Else this function supports recursion. 201 */ 202 critical_enter(); 203 ck_epoch_begin(&record->epoch_record, NULL); 204 ts->rcu_recurse++; 205 if (ts->rcu_recurse == 1) 206 TAILQ_INSERT_TAIL(&record->ts_head, ts, rcu_entry); 207 critical_exit(); 208} 209 210void 211linux_rcu_read_unlock(unsigned type) 212{ 213 struct linux_epoch_record *record; 214 struct task_struct *ts; 215 216 MPASS(type < RCU_TYPE_MAX); 217 218 if (RCU_SKIP()) 219 return; 220 221 record = &DPCPU_GET(linux_epoch_record[type]); 222 ts = current; 223 224 /* 225 * Use a critical section to prevent recursion inside 226 * ck_epoch_end(). Else this function supports recursion. 227 */ 228 critical_enter(); 229 ck_epoch_end(&record->epoch_record, NULL); 230 ts->rcu_recurse--; 231 if (ts->rcu_recurse == 0) 232 TAILQ_REMOVE(&record->ts_head, ts, rcu_entry); 233 critical_exit(); 234 235 sched_unpin(); 236} 237 238static void 239linux_synchronize_rcu_cb(ck_epoch_t *epoch __unused, ck_epoch_record_t *epoch_record, void *arg __unused) 240{ 241 struct linux_epoch_record *record = 242 container_of(epoch_record, struct linux_epoch_record, epoch_record); 243 struct thread *td = curthread; 244 struct task_struct *ts; 245 246 /* check if blocked on the current CPU */ 247 if (record->cpuid == PCPU_GET(cpuid)) { 248 bool is_sleeping = 0; 249 u_char prio = 0; 250 251 /* 252 * Find the lowest priority or sleeping thread which 253 * is blocking synchronization on this CPU core. All 254 * the threads in the queue are CPU-pinned and cannot 255 * go anywhere while the current thread is locked. 256 */ 257 TAILQ_FOREACH(ts, &record->ts_head, rcu_entry) { 258 if (ts->task_thread->td_priority > prio) 259 prio = ts->task_thread->td_priority; 260 is_sleeping |= (ts->task_thread->td_inhibitors != 0); 261 } 262 263 if (is_sleeping) { 264 thread_unlock(td); 265 pause("W", 1); 266 thread_lock(td); 267 } else { 268 /* set new thread priority */ 269 sched_prio(td, prio); 270 /* task switch */ 271 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 272 273 /* 274 * Release the thread lock while yielding to 275 * allow other threads to acquire the lock 276 * pointed to by TDQ_LOCKPTR(td). Else a 277 * deadlock like situation might happen. 278 */ 279 thread_unlock(td); 280 thread_lock(td); 281 } 282 } else { 283 /* 284 * To avoid spinning move execution to the other CPU 285 * which is blocking synchronization. Set highest 286 * thread priority so that code gets run. The thread 287 * priority will be restored later. 288 */ 289 sched_prio(td, 0); 290 sched_bind(td, record->cpuid); 291 } 292} 293 294void 295linux_synchronize_rcu(unsigned type) 296{ 297 struct thread *td; 298 int was_bound; 299 int old_cpu; 300 int old_pinned; 301 u_char old_prio; 302 303 MPASS(type < RCU_TYPE_MAX); 304 305 if (RCU_SKIP()) 306 return; 307 308 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 309 "linux_synchronize_rcu() can sleep"); 310 311 td = curthread; 312 DROP_GIANT(); 313 314 /* 315 * Synchronizing RCU might change the CPU core this function 316 * is running on. Save current values: 317 */ 318 thread_lock(td); 319 320 old_cpu = PCPU_GET(cpuid); 321 old_pinned = td->td_pinned; 322 old_prio = td->td_priority; 323 was_bound = sched_is_bound(td); 324 sched_unbind(td); 325 td->td_pinned = 0; 326 sched_bind(td, old_cpu); 327 328 ck_epoch_synchronize_wait(&linux_epoch[type], 329 &linux_synchronize_rcu_cb, NULL); 330 331 /* restore CPU binding, if any */ 332 if (was_bound != 0) { 333 sched_bind(td, old_cpu); 334 } else { 335 /* get thread back to initial CPU, if any */ 336 if (old_pinned != 0) 337 sched_bind(td, old_cpu); 338 sched_unbind(td); 339 } 340 /* restore pinned after bind */ 341 td->td_pinned = old_pinned; 342 343 /* restore thread priority */ 344 sched_prio(td, old_prio); 345 thread_unlock(td); 346 347 PICKUP_GIANT(); 348} 349 350void 351linux_rcu_barrier(unsigned type) 352{ 353 struct linux_epoch_head *head; 354 355 MPASS(type < RCU_TYPE_MAX); 356 357 linux_synchronize_rcu(type); 358 359 head = &linux_epoch_head[type]; 360 361 /* wait for callbacks to complete */ 362 taskqueue_drain(taskqueue_fast, &head->task); 363} 364 365void 366linux_call_rcu(unsigned type, struct rcu_head *context, rcu_callback_t func) 367{ 368 struct callback_head *rcu; 369 struct linux_epoch_head *head; 370 371 MPASS(type < RCU_TYPE_MAX); 372 373 rcu = (struct callback_head *)context; 374 head = &linux_epoch_head[type]; 375 376 mtx_lock(&head->lock); 377 rcu->func = func; 378 STAILQ_INSERT_TAIL(&head->cb_head, rcu, entry); 379 taskqueue_enqueue(taskqueue_fast, &head->task); 380 mtx_unlock(&head->lock); 381} 382 383int 384init_srcu_struct(struct srcu_struct *srcu) 385{ 386 return (0); 387} 388 389void 390cleanup_srcu_struct(struct srcu_struct *srcu) 391{ 392} 393 394int 395srcu_read_lock(struct srcu_struct *srcu) 396{ 397 linux_rcu_read_lock(RCU_TYPE_SLEEPABLE); 398 return (0); 399} 400 401void 402srcu_read_unlock(struct srcu_struct *srcu, int key __unused) 403{ 404 linux_rcu_read_unlock(RCU_TYPE_SLEEPABLE); 405} 406 407void 408synchronize_srcu(struct srcu_struct *srcu) 409{ 410 linux_synchronize_rcu(RCU_TYPE_SLEEPABLE); 411} 412 413void 414srcu_barrier(struct srcu_struct *srcu) 415{ 416 linux_rcu_barrier(RCU_TYPE_SLEEPABLE); 417} 418