1 /*-
2 * Copyright (c) 2016 Matthew Macy ([email protected])
3 * Copyright (c) 2017-2021 Hans Petter Selasky ([email protected])
4 * All rights reserved.
5 * Copyright (c) 2024 The FreeBSD Foundation
6 *
7 * Portions of this software were developed by Björn Zeeb
8 * under sponsorship from the FreeBSD Foundation.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice unmodified, this list of conditions, and the following
15 * disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
21 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
22 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
23 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
24 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
25 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
29 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 #include <sys/cdefs.h>
33 #include <sys/types.h>
34 #include <sys/systm.h>
35 #include <sys/malloc.h>
36 #include <sys/kernel.h>
37 #include <sys/lock.h>
38 #include <sys/mutex.h>
39 #include <sys/proc.h>
40 #include <sys/sched.h>
41 #include <sys/smp.h>
42 #include <sys/queue.h>
43 #include <sys/taskqueue.h>
44 #include <sys/kdb.h>
45
46 #include <ck_epoch.h>
47
48 #include <linux/rcupdate.h>
49 #include <linux/sched.h>
50 #include <linux/srcu.h>
51 #include <linux/slab.h>
52 #include <linux/kernel.h>
53 #include <linux/compat.h>
54 #include <linux/llist.h>
55 #include <linux/irq_work.h>
56
57 /*
58 * By defining CONFIG_NO_RCU_SKIP LinuxKPI RCU locks and asserts will
59 * not be skipped during panic().
60 */
61 #ifdef CONFIG_NO_RCU_SKIP
62 #define RCU_SKIP(void) 0
63 #else
64 #define RCU_SKIP(void) unlikely(SCHEDULER_STOPPED() || kdb_active)
65 #endif
66
67 struct callback_head {
68 union {
69 STAILQ_ENTRY(callback_head) entry;
70 struct llist_node node;
71 };
72 rcu_callback_t func;
73 };
74
75 struct linux_epoch_head {
76 struct llist_head cb_head;
77 struct task task;
78 } __aligned(CACHE_LINE_SIZE);
79
80 struct linux_epoch_record {
81 ck_epoch_record_t epoch_record;
82 TAILQ_HEAD(, task_struct) ts_head;
83 int cpuid;
84 int type;
85 } __aligned(CACHE_LINE_SIZE);
86
87 /*
88 * Verify that "struct rcu_head" is big enough to hold "struct
89 * callback_head". This has been done to avoid having to add special
90 * compile flags for including ck_epoch.h to all clients of the
91 * LinuxKPI.
92 */
93 CTASSERT(sizeof(struct rcu_head) == sizeof(struct callback_head));
94
95 /*
96 * Verify that "rcu_section[0]" has the same size as
97 * "ck_epoch_section_t". This has been done to avoid having to add
98 * special compile flags for including ck_epoch.h to all clients of
99 * the LinuxKPI.
100 */
101 CTASSERT(sizeof(((struct task_struct *)0)->rcu_section[0] ==
102 sizeof(ck_epoch_section_t)));
103
104 /*
105 * Verify that "epoch_record" is at beginning of "struct
106 * linux_epoch_record":
107 */
108 CTASSERT(offsetof(struct linux_epoch_record, epoch_record) == 0);
109
110 CTASSERT(TS_RCU_TYPE_MAX == RCU_TYPE_MAX);
111
112 static ck_epoch_t linux_epoch[RCU_TYPE_MAX];
113 static struct linux_epoch_head linux_epoch_head[RCU_TYPE_MAX];
114 DPCPU_DEFINE_STATIC(struct linux_epoch_record, linux_epoch_record[RCU_TYPE_MAX]);
115
116 static void linux_rcu_cleaner_func(void *, int);
117
118 static void
linux_rcu_runtime_init(void * arg __unused)119 linux_rcu_runtime_init(void *arg __unused)
120 {
121 struct linux_epoch_head *head;
122 int i;
123 int j;
124
125 for (j = 0; j != RCU_TYPE_MAX; j++) {
126 ck_epoch_init(&linux_epoch[j]);
127
128 head = &linux_epoch_head[j];
129
130 TASK_INIT(&head->task, 0, linux_rcu_cleaner_func, head);
131 init_llist_head(&head->cb_head);
132
133 CPU_FOREACH(i) {
134 struct linux_epoch_record *record;
135
136 record = &DPCPU_ID_GET(i, linux_epoch_record[j]);
137
138 record->cpuid = i;
139 record->type = j;
140 ck_epoch_register(&linux_epoch[j],
141 &record->epoch_record, NULL);
142 TAILQ_INIT(&record->ts_head);
143 }
144 }
145 }
146 SYSINIT(linux_rcu_runtime, SI_SUB_CPU, SI_ORDER_ANY, linux_rcu_runtime_init, NULL);
147
148 static void
linux_rcu_cleaner_func(void * context,int pending __unused)149 linux_rcu_cleaner_func(void *context, int pending __unused)
150 {
151 struct linux_epoch_head *head = context;
152 struct callback_head *rcu;
153 STAILQ_HEAD(, callback_head) tmp_head;
154 struct llist_node *node, *next;
155 uintptr_t offset;
156
157 /* move current callbacks into own queue */
158 STAILQ_INIT(&tmp_head);
159 llist_for_each_safe(node, next, llist_del_all(&head->cb_head)) {
160 rcu = container_of(node, struct callback_head, node);
161 /* re-reverse list to restore chronological order */
162 STAILQ_INSERT_HEAD(&tmp_head, rcu, entry);
163 }
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 STAILQ_REMOVE_HEAD(&tmp_head, entry);
171
172 offset = (uintptr_t)rcu->func;
173
174 if (offset < LINUX_KFREE_RCU_OFFSET_MAX)
175 kfree((char *)rcu - offset);
176 else
177 rcu->func((struct rcu_head *)rcu);
178 }
179 }
180
181 void
linux_rcu_read_lock(unsigned type)182 linux_rcu_read_lock(unsigned type)
183 {
184 struct linux_epoch_record *record;
185 struct task_struct *ts;
186
187 MPASS(type < RCU_TYPE_MAX);
188
189 if (RCU_SKIP())
190 return;
191
192 ts = current;
193
194 /* assert valid refcount */
195 MPASS(ts->rcu_recurse[type] != INT_MAX);
196
197 if (++(ts->rcu_recurse[type]) != 1)
198 return;
199
200 /*
201 * Pin thread to current CPU so that the unlock code gets the
202 * same per-CPU epoch record:
203 */
204 sched_pin();
205
206 record = &DPCPU_GET(linux_epoch_record[type]);
207
208 /*
209 * Use a critical section to prevent recursion inside
210 * ck_epoch_begin(). Else this function supports recursion.
211 */
212 critical_enter();
213 ck_epoch_begin(&record->epoch_record,
214 (ck_epoch_section_t *)&ts->rcu_section[type]);
215 TAILQ_INSERT_TAIL(&record->ts_head, ts, rcu_entry[type]);
216 critical_exit();
217 }
218
219 void
linux_rcu_read_unlock(unsigned type)220 linux_rcu_read_unlock(unsigned type)
221 {
222 struct linux_epoch_record *record;
223 struct task_struct *ts;
224
225 MPASS(type < RCU_TYPE_MAX);
226
227 if (RCU_SKIP())
228 return;
229
230 ts = current;
231
232 /* assert valid refcount */
233 MPASS(ts->rcu_recurse[type] > 0);
234
235 if (--(ts->rcu_recurse[type]) != 0)
236 return;
237
238 record = &DPCPU_GET(linux_epoch_record[type]);
239
240 /*
241 * Use a critical section to prevent recursion inside
242 * ck_epoch_end(). Else this function supports recursion.
243 */
244 critical_enter();
245 ck_epoch_end(&record->epoch_record,
246 (ck_epoch_section_t *)&ts->rcu_section[type]);
247 TAILQ_REMOVE(&record->ts_head, ts, rcu_entry[type]);
248 critical_exit();
249
250 sched_unpin();
251 }
252
253 bool
linux_rcu_read_lock_held(unsigned type)254 linux_rcu_read_lock_held(unsigned type)
255 {
256 #ifdef INVARINATS
257 struct linux_epoch_record *record __diagused;
258 struct task_struct *ts;
259
260 MPASS(type < RCU_TYPE_MAX);
261
262 if (RCU_SKIP())
263 return (false);
264
265 if (__current_unallocated(curthread))
266 return (false);
267
268 ts = current;
269 if (ts->rcu_recurse[type] == 0)
270 return (false);
271
272 MPASS(curthread->td_pinned != 0);
273 MPASS((record = &DPCPU_GET(linux_epoch_record[type])) &&
274 record->epoch_record.active != 0);
275 #endif
276
277 return (true);
278 }
279
280 static void
linux_synchronize_rcu_cb(ck_epoch_t * epoch __unused,ck_epoch_record_t * epoch_record,void * arg __unused)281 linux_synchronize_rcu_cb(ck_epoch_t *epoch __unused, ck_epoch_record_t *epoch_record, void *arg __unused)
282 {
283 struct linux_epoch_record *record =
284 container_of(epoch_record, struct linux_epoch_record, epoch_record);
285 struct thread *td = curthread;
286 struct task_struct *ts;
287
288 /* check if blocked on the current CPU */
289 if (record->cpuid == PCPU_GET(cpuid)) {
290 bool is_sleeping = 0;
291 u_char prio = 0;
292
293 /*
294 * Find the lowest priority or sleeping thread which
295 * is blocking synchronization on this CPU core. All
296 * the threads in the queue are CPU-pinned and cannot
297 * go anywhere while the current thread is locked.
298 */
299 TAILQ_FOREACH(ts, &record->ts_head, rcu_entry[record->type]) {
300 if (ts->task_thread->td_priority > prio)
301 prio = ts->task_thread->td_priority;
302 is_sleeping |= (ts->task_thread->td_inhibitors != 0);
303 }
304
305 if (is_sleeping) {
306 thread_unlock(td);
307 pause("W", 1);
308 thread_lock(td);
309 } else {
310 /* set new thread priority */
311 sched_prio(td, prio);
312 /* task switch */
313 mi_switch(SW_VOL | SWT_RELINQUISH);
314 /*
315 * It is important the thread lock is dropped
316 * while yielding to allow other threads to
317 * acquire the lock pointed to by
318 * TDQ_LOCKPTR(td). Currently mi_switch() will
319 * unlock the thread lock before
320 * returning. Else a deadlock like situation
321 * might happen.
322 */
323 thread_lock(td);
324 }
325 } else {
326 /*
327 * To avoid spinning move execution to the other CPU
328 * which is blocking synchronization. Set highest
329 * thread priority so that code gets run. The thread
330 * priority will be restored later.
331 */
332 sched_prio(td, 0);
333 sched_bind(td, record->cpuid);
334 }
335 }
336
337 void
linux_synchronize_rcu(unsigned type)338 linux_synchronize_rcu(unsigned type)
339 {
340 struct thread *td;
341 int was_bound;
342 int old_cpu;
343 int old_pinned;
344 u_char old_prio;
345
346 MPASS(type < RCU_TYPE_MAX);
347
348 if (RCU_SKIP())
349 return;
350
351 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
352 "linux_synchronize_rcu() can sleep");
353
354 td = curthread;
355 DROP_GIANT();
356
357 /*
358 * Synchronizing RCU might change the CPU core this function
359 * is running on. Save current values:
360 */
361 thread_lock(td);
362
363 old_cpu = PCPU_GET(cpuid);
364 old_pinned = td->td_pinned;
365 old_prio = td->td_priority;
366 was_bound = sched_is_bound(td);
367 sched_unbind(td);
368 td->td_pinned = 0;
369 sched_bind(td, old_cpu);
370
371 ck_epoch_synchronize_wait(&linux_epoch[type],
372 &linux_synchronize_rcu_cb, NULL);
373
374 /* restore CPU binding, if any */
375 if (was_bound != 0) {
376 sched_bind(td, old_cpu);
377 } else {
378 /* get thread back to initial CPU, if any */
379 if (old_pinned != 0)
380 sched_bind(td, old_cpu);
381 sched_unbind(td);
382 }
383 /* restore pinned after bind */
384 td->td_pinned = old_pinned;
385
386 /* restore thread priority */
387 sched_prio(td, old_prio);
388 thread_unlock(td);
389
390 PICKUP_GIANT();
391 }
392
393 void
linux_rcu_barrier(unsigned type)394 linux_rcu_barrier(unsigned type)
395 {
396 struct linux_epoch_head *head;
397
398 MPASS(type < RCU_TYPE_MAX);
399
400 /*
401 * This function is not obligated to wait for a grace period.
402 * It only waits for RCU callbacks that have already been posted.
403 * If there are no RCU callbacks posted, rcu_barrier() can return
404 * immediately.
405 */
406 head = &linux_epoch_head[type];
407
408 /* wait for callbacks to complete */
409 taskqueue_drain(linux_irq_work_tq, &head->task);
410 }
411
412 void
linux_call_rcu(unsigned type,struct rcu_head * context,rcu_callback_t func)413 linux_call_rcu(unsigned type, struct rcu_head *context, rcu_callback_t func)
414 {
415 struct callback_head *rcu;
416 struct linux_epoch_head *head;
417
418 MPASS(type < RCU_TYPE_MAX);
419
420 rcu = (struct callback_head *)context;
421 head = &linux_epoch_head[type];
422
423 rcu->func = func;
424 llist_add(&rcu->node, &head->cb_head);
425 taskqueue_enqueue(linux_irq_work_tq, &head->task);
426 }
427
428 int
init_srcu_struct(struct srcu_struct * srcu)429 init_srcu_struct(struct srcu_struct *srcu)
430 {
431 return (0);
432 }
433
434 void
cleanup_srcu_struct(struct srcu_struct * srcu)435 cleanup_srcu_struct(struct srcu_struct *srcu)
436 {
437 }
438
439 int
srcu_read_lock(struct srcu_struct * srcu)440 srcu_read_lock(struct srcu_struct *srcu)
441 {
442 linux_rcu_read_lock(RCU_TYPE_SLEEPABLE);
443 return (0);
444 }
445
446 void
srcu_read_unlock(struct srcu_struct * srcu,int key __unused)447 srcu_read_unlock(struct srcu_struct *srcu, int key __unused)
448 {
449 linux_rcu_read_unlock(RCU_TYPE_SLEEPABLE);
450 }
451
452 void
synchronize_srcu(struct srcu_struct * srcu)453 synchronize_srcu(struct srcu_struct *srcu)
454 {
455 linux_synchronize_rcu(RCU_TYPE_SLEEPABLE);
456 }
457
458 void
srcu_barrier(struct srcu_struct * srcu)459 srcu_barrier(struct srcu_struct *srcu)
460 {
461 linux_rcu_barrier(RCU_TYPE_SLEEPABLE);
462 }
463