linux_rcu.c revision 364391
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 364391 2020-08-19 13:35:32Z 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 int type; 78} __aligned(CACHE_LINE_SIZE); 79 80/* 81 * Verify that "struct rcu_head" is big enough to hold "struct 82 * callback_head". This has been done to avoid having to add special 83 * compile flags for including ck_epoch.h to all clients of the 84 * LinuxKPI. 85 */ 86CTASSERT(sizeof(struct rcu_head) == sizeof(struct callback_head)); 87 88/* 89 * Verify that "epoch_record" is at beginning of "struct 90 * linux_epoch_record": 91 */ 92CTASSERT(offsetof(struct linux_epoch_record, epoch_record) == 0); 93 94CTASSERT(TS_RCU_TYPE_MAX == RCU_TYPE_MAX); 95 96static ck_epoch_t linux_epoch[RCU_TYPE_MAX]; 97static struct linux_epoch_head linux_epoch_head[RCU_TYPE_MAX]; 98static DPCPU_DEFINE(struct linux_epoch_record, linux_epoch_record[RCU_TYPE_MAX]); 99 100static void linux_rcu_cleaner_func(void *, int); 101 102static void 103linux_rcu_runtime_init(void *arg __unused) 104{ 105 struct linux_epoch_head *head; 106 int i; 107 int j; 108 109 for (j = 0; j != RCU_TYPE_MAX; j++) { 110 ck_epoch_init(&linux_epoch[j]); 111 112 head = &linux_epoch_head[j]; 113 114 mtx_init(&head->lock, "LRCU-HEAD", NULL, MTX_DEF); 115 TASK_INIT(&head->task, 0, linux_rcu_cleaner_func, head); 116 STAILQ_INIT(&head->cb_head); 117 118 CPU_FOREACH(i) { 119 struct linux_epoch_record *record; 120 121 record = &DPCPU_ID_GET(i, linux_epoch_record[j]); 122 123 record->cpuid = i; 124 record->type = j; 125 ck_epoch_register(&linux_epoch[j], 126 &record->epoch_record, NULL); 127 TAILQ_INIT(&record->ts_head); 128 } 129 } 130} 131SYSINIT(linux_rcu_runtime, SI_SUB_CPU, SI_ORDER_ANY, linux_rcu_runtime_init, NULL); 132 133static void 134linux_rcu_runtime_uninit(void *arg __unused) 135{ 136 struct linux_epoch_head *head; 137 int j; 138 139 for (j = 0; j != RCU_TYPE_MAX; j++) { 140 head = &linux_epoch_head[j]; 141 142 mtx_destroy(&head->lock); 143 } 144} 145SYSUNINIT(linux_rcu_runtime, SI_SUB_LOCK, SI_ORDER_SECOND, linux_rcu_runtime_uninit, NULL); 146 147static void 148linux_rcu_cleaner_func(void *context, int pending __unused) 149{ 150 struct linux_epoch_head *head; 151 struct callback_head *rcu; 152 STAILQ_HEAD(, callback_head) tmp_head; 153 uintptr_t offset; 154 155 linux_set_current(curthread); 156 157 head = context; 158 159 /* move current callbacks into own queue */ 160 mtx_lock(&head->lock); 161 STAILQ_INIT(&tmp_head); 162 STAILQ_CONCAT(&tmp_head, &head->cb_head); 163 mtx_unlock(&head->lock); 164 165 /* synchronize */ 166 linux_synchronize_rcu(head - linux_epoch_head); 167 168 /* dispatch all callbacks, if any */ 169 while ((rcu = STAILQ_FIRST(&tmp_head)) != NULL) { 170 171 STAILQ_REMOVE_HEAD(&tmp_head, entry); 172 173 offset = (uintptr_t)rcu->func; 174 175 if (offset < LINUX_KFREE_RCU_OFFSET_MAX) 176 kfree((char *)rcu - offset); 177 else 178 rcu->func((struct rcu_head *)rcu); 179 } 180} 181 182void 183linux_rcu_read_lock(unsigned type) 184{ 185 struct linux_epoch_record *record; 186 struct task_struct *ts; 187 188 MPASS(type < RCU_TYPE_MAX); 189 190 if (RCU_SKIP()) 191 return; 192 193 /* 194 * Pin thread to current CPU so that the unlock code gets the 195 * same per-CPU epoch record: 196 */ 197 sched_pin(); 198 199 record = &DPCPU_GET(linux_epoch_record[type]); 200 ts = current; 201 202 /* 203 * Use a critical section to prevent recursion inside 204 * ck_epoch_begin(). Else this function supports recursion. 205 */ 206 critical_enter(); 207 ck_epoch_begin(&record->epoch_record, NULL); 208 ts->rcu_recurse[type]++; 209 if (ts->rcu_recurse[type] == 1) 210 TAILQ_INSERT_TAIL(&record->ts_head, ts, rcu_entry[type]); 211 critical_exit(); 212} 213 214void 215linux_rcu_read_unlock(unsigned type) 216{ 217 struct linux_epoch_record *record; 218 struct task_struct *ts; 219 220 MPASS(type < RCU_TYPE_MAX); 221 222 if (RCU_SKIP()) 223 return; 224 225 record = &DPCPU_GET(linux_epoch_record[type]); 226 ts = current; 227 228 /* 229 * Use a critical section to prevent recursion inside 230 * ck_epoch_end(). Else this function supports recursion. 231 */ 232 critical_enter(); 233 ck_epoch_end(&record->epoch_record, NULL); 234 ts->rcu_recurse[type]--; 235 if (ts->rcu_recurse[type] == 0) 236 TAILQ_REMOVE(&record->ts_head, ts, rcu_entry[type]); 237 critical_exit(); 238 239 sched_unpin(); 240} 241 242static void 243linux_synchronize_rcu_cb(ck_epoch_t *epoch __unused, ck_epoch_record_t *epoch_record, void *arg __unused) 244{ 245 struct linux_epoch_record *record = 246 container_of(epoch_record, struct linux_epoch_record, epoch_record); 247 struct thread *td = curthread; 248 struct task_struct *ts; 249 250 /* check if blocked on the current CPU */ 251 if (record->cpuid == PCPU_GET(cpuid)) { 252 bool is_sleeping = 0; 253 u_char prio = 0; 254 255 /* 256 * Find the lowest priority or sleeping thread which 257 * is blocking synchronization on this CPU core. All 258 * the threads in the queue are CPU-pinned and cannot 259 * go anywhere while the current thread is locked. 260 */ 261 TAILQ_FOREACH(ts, &record->ts_head, rcu_entry[record->type]) { 262 if (ts->task_thread->td_priority > prio) 263 prio = ts->task_thread->td_priority; 264 is_sleeping |= (ts->task_thread->td_inhibitors != 0); 265 } 266 267 if (is_sleeping) { 268 thread_unlock(td); 269 pause("W", 1); 270 thread_lock(td); 271 } else { 272 /* set new thread priority */ 273 sched_prio(td, prio); 274 /* task switch */ 275 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 276 277 /* 278 * Release the thread lock while yielding to 279 * allow other threads to acquire the lock 280 * pointed to by TDQ_LOCKPTR(td). Else a 281 * deadlock like situation might happen. 282 */ 283 thread_unlock(td); 284 thread_lock(td); 285 } 286 } else { 287 /* 288 * To avoid spinning move execution to the other CPU 289 * which is blocking synchronization. Set highest 290 * thread priority so that code gets run. The thread 291 * priority will be restored later. 292 */ 293 sched_prio(td, 0); 294 sched_bind(td, record->cpuid); 295 } 296} 297 298void 299linux_synchronize_rcu(unsigned type) 300{ 301 struct thread *td; 302 int was_bound; 303 int old_cpu; 304 int old_pinned; 305 u_char old_prio; 306 307 MPASS(type < RCU_TYPE_MAX); 308 309 if (RCU_SKIP()) 310 return; 311 312 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 313 "linux_synchronize_rcu() can sleep"); 314 315 td = curthread; 316 DROP_GIANT(); 317 318 /* 319 * Synchronizing RCU might change the CPU core this function 320 * is running on. Save current values: 321 */ 322 thread_lock(td); 323 324 old_cpu = PCPU_GET(cpuid); 325 old_pinned = td->td_pinned; 326 old_prio = td->td_priority; 327 was_bound = sched_is_bound(td); 328 sched_unbind(td); 329 td->td_pinned = 0; 330 sched_bind(td, old_cpu); 331 332 ck_epoch_synchronize_wait(&linux_epoch[type], 333 &linux_synchronize_rcu_cb, NULL); 334 335 /* restore CPU binding, if any */ 336 if (was_bound != 0) { 337 sched_bind(td, old_cpu); 338 } else { 339 /* get thread back to initial CPU, if any */ 340 if (old_pinned != 0) 341 sched_bind(td, old_cpu); 342 sched_unbind(td); 343 } 344 /* restore pinned after bind */ 345 td->td_pinned = old_pinned; 346 347 /* restore thread priority */ 348 sched_prio(td, old_prio); 349 thread_unlock(td); 350 351 PICKUP_GIANT(); 352} 353 354void 355linux_rcu_barrier(unsigned type) 356{ 357 struct linux_epoch_head *head; 358 359 MPASS(type < RCU_TYPE_MAX); 360 361 linux_synchronize_rcu(type); 362 363 head = &linux_epoch_head[type]; 364 365 /* wait for callbacks to complete */ 366 taskqueue_drain(taskqueue_fast, &head->task); 367} 368 369void 370linux_call_rcu(unsigned type, struct rcu_head *context, rcu_callback_t func) 371{ 372 struct callback_head *rcu; 373 struct linux_epoch_head *head; 374 375 MPASS(type < RCU_TYPE_MAX); 376 377 rcu = (struct callback_head *)context; 378 head = &linux_epoch_head[type]; 379 380 mtx_lock(&head->lock); 381 rcu->func = func; 382 STAILQ_INSERT_TAIL(&head->cb_head, rcu, entry); 383 taskqueue_enqueue(taskqueue_fast, &head->task); 384 mtx_unlock(&head->lock); 385} 386 387int 388init_srcu_struct(struct srcu_struct *srcu) 389{ 390 return (0); 391} 392 393void 394cleanup_srcu_struct(struct srcu_struct *srcu) 395{ 396} 397 398int 399srcu_read_lock(struct srcu_struct *srcu) 400{ 401 linux_rcu_read_lock(RCU_TYPE_SLEEPABLE); 402 return (0); 403} 404 405void 406srcu_read_unlock(struct srcu_struct *srcu, int key __unused) 407{ 408 linux_rcu_read_unlock(RCU_TYPE_SLEEPABLE); 409} 410 411void 412synchronize_srcu(struct srcu_struct *srcu) 413{ 414 linux_synchronize_rcu(RCU_TYPE_SLEEPABLE); 415} 416 417void 418srcu_barrier(struct srcu_struct *srcu) 419{ 420 linux_rcu_barrier(RCU_TYPE_SLEEPABLE); 421} 422