1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* |
3 | * Copyright (C) 2010-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
4 | * |
5 | * membarrier system call |
6 | */ |
7 | |
8 | /* |
9 | * For documentation purposes, here are some membarrier ordering |
10 | * scenarios to keep in mind: |
11 | * |
12 | * A) Userspace thread execution after IPI vs membarrier's memory |
13 | * barrier before sending the IPI |
14 | * |
15 | * Userspace variables: |
16 | * |
17 | * int x = 0, y = 0; |
18 | * |
19 | * The memory barrier at the start of membarrier() on CPU0 is necessary in |
20 | * order to enforce the guarantee that any writes occurring on CPU0 before |
21 | * the membarrier() is executed will be visible to any code executing on |
22 | * CPU1 after the IPI-induced memory barrier: |
23 | * |
24 | * CPU0 CPU1 |
25 | * |
26 | * x = 1 |
27 | * membarrier(): |
28 | * a: smp_mb() |
29 | * b: send IPI IPI-induced mb |
30 | * c: smp_mb() |
31 | * r2 = y |
32 | * y = 1 |
33 | * barrier() |
34 | * r1 = x |
35 | * |
36 | * BUG_ON(r1 == 0 && r2 == 0) |
37 | * |
38 | * The write to y and load from x by CPU1 are unordered by the hardware, |
39 | * so it's possible to have "r1 = x" reordered before "y = 1" at any |
40 | * point after (b). If the memory barrier at (a) is omitted, then "x = 1" |
41 | * can be reordered after (a) (although not after (c)), so we get r1 == 0 |
42 | * and r2 == 0. This violates the guarantee that membarrier() is |
43 | * supposed by provide. |
44 | * |
45 | * The timing of the memory barrier at (a) has to ensure that it executes |
46 | * before the IPI-induced memory barrier on CPU1. |
47 | * |
48 | * B) Userspace thread execution before IPI vs membarrier's memory |
49 | * barrier after completing the IPI |
50 | * |
51 | * Userspace variables: |
52 | * |
53 | * int x = 0, y = 0; |
54 | * |
55 | * The memory barrier at the end of membarrier() on CPU0 is necessary in |
56 | * order to enforce the guarantee that any writes occurring on CPU1 before |
57 | * the membarrier() is executed will be visible to any code executing on |
58 | * CPU0 after the membarrier(): |
59 | * |
60 | * CPU0 CPU1 |
61 | * |
62 | * x = 1 |
63 | * barrier() |
64 | * y = 1 |
65 | * r2 = y |
66 | * membarrier(): |
67 | * a: smp_mb() |
68 | * b: send IPI IPI-induced mb |
69 | * c: smp_mb() |
70 | * r1 = x |
71 | * BUG_ON(r1 == 0 && r2 == 1) |
72 | * |
73 | * The writes to x and y are unordered by the hardware, so it's possible to |
74 | * have "r2 = 1" even though the write to x doesn't execute until (b). If |
75 | * the memory barrier at (c) is omitted then "r1 = x" can be reordered |
76 | * before (b) (although not before (a)), so we get "r1 = 0". This violates |
77 | * the guarantee that membarrier() is supposed to provide. |
78 | * |
79 | * The timing of the memory barrier at (c) has to ensure that it executes |
80 | * after the IPI-induced memory barrier on CPU1. |
81 | * |
82 | * C) Scheduling userspace thread -> kthread -> userspace thread vs membarrier |
83 | * |
84 | * CPU0 CPU1 |
85 | * |
86 | * membarrier(): |
87 | * a: smp_mb() |
88 | * d: switch to kthread (includes mb) |
89 | * b: read rq->curr->mm == NULL |
90 | * e: switch to user (includes mb) |
91 | * c: smp_mb() |
92 | * |
93 | * Using the scenario from (A), we can show that (a) needs to be paired |
94 | * with (e). Using the scenario from (B), we can show that (c) needs to |
95 | * be paired with (d). |
96 | * |
97 | * D) exit_mm vs membarrier |
98 | * |
99 | * Two thread groups are created, A and B. Thread group B is created by |
100 | * issuing clone from group A with flag CLONE_VM set, but not CLONE_THREAD. |
101 | * Let's assume we have a single thread within each thread group (Thread A |
102 | * and Thread B). Thread A runs on CPU0, Thread B runs on CPU1. |
103 | * |
104 | * CPU0 CPU1 |
105 | * |
106 | * membarrier(): |
107 | * a: smp_mb() |
108 | * exit_mm(): |
109 | * d: smp_mb() |
110 | * e: current->mm = NULL |
111 | * b: read rq->curr->mm == NULL |
112 | * c: smp_mb() |
113 | * |
114 | * Using scenario (B), we can show that (c) needs to be paired with (d). |
115 | * |
116 | * E) kthread_{use,unuse}_mm vs membarrier |
117 | * |
118 | * CPU0 CPU1 |
119 | * |
120 | * membarrier(): |
121 | * a: smp_mb() |
122 | * kthread_unuse_mm() |
123 | * d: smp_mb() |
124 | * e: current->mm = NULL |
125 | * b: read rq->curr->mm == NULL |
126 | * kthread_use_mm() |
127 | * f: current->mm = mm |
128 | * g: smp_mb() |
129 | * c: smp_mb() |
130 | * |
131 | * Using the scenario from (A), we can show that (a) needs to be paired |
132 | * with (g). Using the scenario from (B), we can show that (c) needs to |
133 | * be paired with (d). |
134 | */ |
135 | |
136 | /* |
137 | * Bitmask made from a "or" of all commands within enum membarrier_cmd, |
138 | * except MEMBARRIER_CMD_QUERY. |
139 | */ |
140 | #ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE |
141 | #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \ |
142 | (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \ |
143 | | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE) |
144 | #else |
145 | #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0 |
146 | #endif |
147 | |
148 | #ifdef CONFIG_RSEQ |
149 | #define MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK \ |
150 | (MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ \ |
151 | | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ) |
152 | #else |
153 | #define MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK 0 |
154 | #endif |
155 | |
156 | #define MEMBARRIER_CMD_BITMASK \ |
157 | (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \ |
158 | | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \ |
159 | | MEMBARRIER_CMD_PRIVATE_EXPEDITED \ |
160 | | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \ |
161 | | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \ |
162 | | MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK \ |
163 | | MEMBARRIER_CMD_GET_REGISTRATIONS) |
164 | |
165 | static void ipi_mb(void *info) |
166 | { |
167 | smp_mb(); /* IPIs should be serializing but paranoid. */ |
168 | } |
169 | |
170 | static void ipi_sync_core(void *info) |
171 | { |
172 | /* |
173 | * The smp_mb() in membarrier after all the IPIs is supposed to |
174 | * ensure that memory on remote CPUs that occur before the IPI |
175 | * become visible to membarrier()'s caller -- see scenario B in |
176 | * the big comment at the top of this file. |
177 | * |
178 | * A sync_core() would provide this guarantee, but |
179 | * sync_core_before_usermode() might end up being deferred until |
180 | * after membarrier()'s smp_mb(). |
181 | */ |
182 | smp_mb(); /* IPIs should be serializing but paranoid. */ |
183 | |
184 | sync_core_before_usermode(); |
185 | } |
186 | |
187 | static void ipi_rseq(void *info) |
188 | { |
189 | /* |
190 | * Ensure that all stores done by the calling thread are visible |
191 | * to the current task before the current task resumes. We could |
192 | * probably optimize this away on most architectures, but by the |
193 | * time we've already sent an IPI, the cost of the extra smp_mb() |
194 | * is negligible. |
195 | */ |
196 | smp_mb(); |
197 | rseq_preempt(current); |
198 | } |
199 | |
200 | static void ipi_sync_rq_state(void *info) |
201 | { |
202 | struct mm_struct *mm = (struct mm_struct *) info; |
203 | |
204 | if (current->mm != mm) |
205 | return; |
206 | this_cpu_write(runqueues.membarrier_state, |
207 | atomic_read(&mm->membarrier_state)); |
208 | /* |
209 | * Issue a memory barrier after setting |
210 | * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to |
211 | * guarantee that no memory access following registration is reordered |
212 | * before registration. |
213 | */ |
214 | smp_mb(); |
215 | } |
216 | |
217 | void membarrier_exec_mmap(struct mm_struct *mm) |
218 | { |
219 | /* |
220 | * Issue a memory barrier before clearing membarrier_state to |
221 | * guarantee that no memory access prior to exec is reordered after |
222 | * clearing this state. |
223 | */ |
224 | smp_mb(); |
225 | atomic_set(v: &mm->membarrier_state, i: 0); |
226 | /* |
227 | * Keep the runqueue membarrier_state in sync with this mm |
228 | * membarrier_state. |
229 | */ |
230 | this_cpu_write(runqueues.membarrier_state, 0); |
231 | } |
232 | |
233 | void membarrier_update_current_mm(struct mm_struct *next_mm) |
234 | { |
235 | struct rq *rq = this_rq(); |
236 | int membarrier_state = 0; |
237 | |
238 | if (next_mm) |
239 | membarrier_state = atomic_read(v: &next_mm->membarrier_state); |
240 | if (READ_ONCE(rq->membarrier_state) == membarrier_state) |
241 | return; |
242 | WRITE_ONCE(rq->membarrier_state, membarrier_state); |
243 | } |
244 | |
245 | static int membarrier_global_expedited(void) |
246 | { |
247 | int cpu; |
248 | cpumask_var_t tmpmask; |
249 | |
250 | if (num_online_cpus() == 1) |
251 | return 0; |
252 | |
253 | /* |
254 | * Matches memory barriers around rq->curr modification in |
255 | * scheduler. |
256 | */ |
257 | smp_mb(); /* system call entry is not a mb. */ |
258 | |
259 | if (!zalloc_cpumask_var(mask: &tmpmask, GFP_KERNEL)) |
260 | return -ENOMEM; |
261 | |
262 | cpus_read_lock(); |
263 | rcu_read_lock(); |
264 | for_each_online_cpu(cpu) { |
265 | struct task_struct *p; |
266 | |
267 | /* |
268 | * Skipping the current CPU is OK even through we can be |
269 | * migrated at any point. The current CPU, at the point |
270 | * where we read raw_smp_processor_id(), is ensured to |
271 | * be in program order with respect to the caller |
272 | * thread. Therefore, we can skip this CPU from the |
273 | * iteration. |
274 | */ |
275 | if (cpu == raw_smp_processor_id()) |
276 | continue; |
277 | |
278 | if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) & |
279 | MEMBARRIER_STATE_GLOBAL_EXPEDITED)) |
280 | continue; |
281 | |
282 | /* |
283 | * Skip the CPU if it runs a kernel thread which is not using |
284 | * a task mm. |
285 | */ |
286 | p = rcu_dereference(cpu_rq(cpu)->curr); |
287 | if (!p->mm) |
288 | continue; |
289 | |
290 | __cpumask_set_cpu(cpu, dstp: tmpmask); |
291 | } |
292 | rcu_read_unlock(); |
293 | |
294 | preempt_disable(); |
295 | smp_call_function_many(mask: tmpmask, func: ipi_mb, NULL, wait: 1); |
296 | preempt_enable(); |
297 | |
298 | free_cpumask_var(mask: tmpmask); |
299 | cpus_read_unlock(); |
300 | |
301 | /* |
302 | * Memory barrier on the caller thread _after_ we finished |
303 | * waiting for the last IPI. Matches memory barriers around |
304 | * rq->curr modification in scheduler. |
305 | */ |
306 | smp_mb(); /* exit from system call is not a mb */ |
307 | return 0; |
308 | } |
309 | |
310 | static int membarrier_private_expedited(int flags, int cpu_id) |
311 | { |
312 | cpumask_var_t tmpmask; |
313 | struct mm_struct *mm = current->mm; |
314 | smp_call_func_t ipi_func = ipi_mb; |
315 | |
316 | if (flags == MEMBARRIER_FLAG_SYNC_CORE) { |
317 | if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) |
318 | return -EINVAL; |
319 | if (!(atomic_read(v: &mm->membarrier_state) & |
320 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY)) |
321 | return -EPERM; |
322 | ipi_func = ipi_sync_core; |
323 | } else if (flags == MEMBARRIER_FLAG_RSEQ) { |
324 | if (!IS_ENABLED(CONFIG_RSEQ)) |
325 | return -EINVAL; |
326 | if (!(atomic_read(v: &mm->membarrier_state) & |
327 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY)) |
328 | return -EPERM; |
329 | ipi_func = ipi_rseq; |
330 | } else { |
331 | WARN_ON_ONCE(flags); |
332 | if (!(atomic_read(v: &mm->membarrier_state) & |
333 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY)) |
334 | return -EPERM; |
335 | } |
336 | |
337 | if (flags != MEMBARRIER_FLAG_SYNC_CORE && |
338 | (atomic_read(v: &mm->mm_users) == 1 || num_online_cpus() == 1)) |
339 | return 0; |
340 | |
341 | /* |
342 | * Matches memory barriers around rq->curr modification in |
343 | * scheduler. |
344 | */ |
345 | smp_mb(); /* system call entry is not a mb. */ |
346 | |
347 | if (cpu_id < 0 && !zalloc_cpumask_var(mask: &tmpmask, GFP_KERNEL)) |
348 | return -ENOMEM; |
349 | |
350 | cpus_read_lock(); |
351 | |
352 | if (cpu_id >= 0) { |
353 | struct task_struct *p; |
354 | |
355 | if (cpu_id >= nr_cpu_ids || !cpu_online(cpu: cpu_id)) |
356 | goto out; |
357 | rcu_read_lock(); |
358 | p = rcu_dereference(cpu_rq(cpu_id)->curr); |
359 | if (!p || p->mm != mm) { |
360 | rcu_read_unlock(); |
361 | goto out; |
362 | } |
363 | rcu_read_unlock(); |
364 | } else { |
365 | int cpu; |
366 | |
367 | rcu_read_lock(); |
368 | for_each_online_cpu(cpu) { |
369 | struct task_struct *p; |
370 | |
371 | p = rcu_dereference(cpu_rq(cpu)->curr); |
372 | if (p && p->mm == mm) |
373 | __cpumask_set_cpu(cpu, dstp: tmpmask); |
374 | } |
375 | rcu_read_unlock(); |
376 | } |
377 | |
378 | if (cpu_id >= 0) { |
379 | /* |
380 | * smp_call_function_single() will call ipi_func() if cpu_id |
381 | * is the calling CPU. |
382 | */ |
383 | smp_call_function_single(cpuid: cpu_id, func: ipi_func, NULL, wait: 1); |
384 | } else { |
385 | /* |
386 | * For regular membarrier, we can save a few cycles by |
387 | * skipping the current cpu -- we're about to do smp_mb() |
388 | * below, and if we migrate to a different cpu, this cpu |
389 | * and the new cpu will execute a full barrier in the |
390 | * scheduler. |
391 | * |
392 | * For SYNC_CORE, we do need a barrier on the current cpu -- |
393 | * otherwise, if we are migrated and replaced by a different |
394 | * task in the same mm just before, during, or after |
395 | * membarrier, we will end up with some thread in the mm |
396 | * running without a core sync. |
397 | * |
398 | * For RSEQ, don't rseq_preempt() the caller. User code |
399 | * is not supposed to issue syscalls at all from inside an |
400 | * rseq critical section. |
401 | */ |
402 | if (flags != MEMBARRIER_FLAG_SYNC_CORE) { |
403 | preempt_disable(); |
404 | smp_call_function_many(mask: tmpmask, func: ipi_func, NULL, wait: true); |
405 | preempt_enable(); |
406 | } else { |
407 | on_each_cpu_mask(mask: tmpmask, func: ipi_func, NULL, wait: true); |
408 | } |
409 | } |
410 | |
411 | out: |
412 | if (cpu_id < 0) |
413 | free_cpumask_var(mask: tmpmask); |
414 | cpus_read_unlock(); |
415 | |
416 | /* |
417 | * Memory barrier on the caller thread _after_ we finished |
418 | * waiting for the last IPI. Matches memory barriers around |
419 | * rq->curr modification in scheduler. |
420 | */ |
421 | smp_mb(); /* exit from system call is not a mb */ |
422 | |
423 | return 0; |
424 | } |
425 | |
426 | static int sync_runqueues_membarrier_state(struct mm_struct *mm) |
427 | { |
428 | int membarrier_state = atomic_read(v: &mm->membarrier_state); |
429 | cpumask_var_t tmpmask; |
430 | int cpu; |
431 | |
432 | if (atomic_read(v: &mm->mm_users) == 1 || num_online_cpus() == 1) { |
433 | this_cpu_write(runqueues.membarrier_state, membarrier_state); |
434 | |
435 | /* |
436 | * For single mm user, we can simply issue a memory barrier |
437 | * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the |
438 | * mm and in the current runqueue to guarantee that no memory |
439 | * access following registration is reordered before |
440 | * registration. |
441 | */ |
442 | smp_mb(); |
443 | return 0; |
444 | } |
445 | |
446 | if (!zalloc_cpumask_var(mask: &tmpmask, GFP_KERNEL)) |
447 | return -ENOMEM; |
448 | |
449 | /* |
450 | * For mm with multiple users, we need to ensure all future |
451 | * scheduler executions will observe @mm's new membarrier |
452 | * state. |
453 | */ |
454 | synchronize_rcu(); |
455 | |
456 | /* |
457 | * For each cpu runqueue, if the task's mm match @mm, ensure that all |
458 | * @mm's membarrier state set bits are also set in the runqueue's |
459 | * membarrier state. This ensures that a runqueue scheduling |
460 | * between threads which are users of @mm has its membarrier state |
461 | * updated. |
462 | */ |
463 | cpus_read_lock(); |
464 | rcu_read_lock(); |
465 | for_each_online_cpu(cpu) { |
466 | struct rq *rq = cpu_rq(cpu); |
467 | struct task_struct *p; |
468 | |
469 | p = rcu_dereference(rq->curr); |
470 | if (p && p->mm == mm) |
471 | __cpumask_set_cpu(cpu, dstp: tmpmask); |
472 | } |
473 | rcu_read_unlock(); |
474 | |
475 | on_each_cpu_mask(mask: tmpmask, func: ipi_sync_rq_state, info: mm, wait: true); |
476 | |
477 | free_cpumask_var(mask: tmpmask); |
478 | cpus_read_unlock(); |
479 | |
480 | return 0; |
481 | } |
482 | |
483 | static int membarrier_register_global_expedited(void) |
484 | { |
485 | struct task_struct *p = current; |
486 | struct mm_struct *mm = p->mm; |
487 | int ret; |
488 | |
489 | if (atomic_read(v: &mm->membarrier_state) & |
490 | MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY) |
491 | return 0; |
492 | atomic_or(i: MEMBARRIER_STATE_GLOBAL_EXPEDITED, v: &mm->membarrier_state); |
493 | ret = sync_runqueues_membarrier_state(mm); |
494 | if (ret) |
495 | return ret; |
496 | atomic_or(i: MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY, |
497 | v: &mm->membarrier_state); |
498 | |
499 | return 0; |
500 | } |
501 | |
502 | static int membarrier_register_private_expedited(int flags) |
503 | { |
504 | struct task_struct *p = current; |
505 | struct mm_struct *mm = p->mm; |
506 | int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY, |
507 | set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED, |
508 | ret; |
509 | |
510 | if (flags == MEMBARRIER_FLAG_SYNC_CORE) { |
511 | if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) |
512 | return -EINVAL; |
513 | ready_state = |
514 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; |
515 | } else if (flags == MEMBARRIER_FLAG_RSEQ) { |
516 | if (!IS_ENABLED(CONFIG_RSEQ)) |
517 | return -EINVAL; |
518 | ready_state = |
519 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY; |
520 | } else { |
521 | WARN_ON_ONCE(flags); |
522 | } |
523 | |
524 | /* |
525 | * We need to consider threads belonging to different thread |
526 | * groups, which use the same mm. (CLONE_VM but not |
527 | * CLONE_THREAD). |
528 | */ |
529 | if ((atomic_read(v: &mm->membarrier_state) & ready_state) == ready_state) |
530 | return 0; |
531 | if (flags & MEMBARRIER_FLAG_SYNC_CORE) |
532 | set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE; |
533 | if (flags & MEMBARRIER_FLAG_RSEQ) |
534 | set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ; |
535 | atomic_or(i: set_state, v: &mm->membarrier_state); |
536 | ret = sync_runqueues_membarrier_state(mm); |
537 | if (ret) |
538 | return ret; |
539 | atomic_or(i: ready_state, v: &mm->membarrier_state); |
540 | |
541 | return 0; |
542 | } |
543 | |
544 | static int membarrier_get_registrations(void) |
545 | { |
546 | struct task_struct *p = current; |
547 | struct mm_struct *mm = p->mm; |
548 | int registrations_mask = 0, membarrier_state, i; |
549 | static const int states[] = { |
550 | MEMBARRIER_STATE_GLOBAL_EXPEDITED | |
551 | MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY, |
552 | MEMBARRIER_STATE_PRIVATE_EXPEDITED | |
553 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY, |
554 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE | |
555 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY, |
556 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ | |
557 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY |
558 | }; |
559 | static const int registration_cmds[] = { |
560 | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, |
561 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, |
562 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE, |
563 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ |
564 | }; |
565 | BUILD_BUG_ON(ARRAY_SIZE(states) != ARRAY_SIZE(registration_cmds)); |
566 | |
567 | membarrier_state = atomic_read(v: &mm->membarrier_state); |
568 | for (i = 0; i < ARRAY_SIZE(states); ++i) { |
569 | if (membarrier_state & states[i]) { |
570 | registrations_mask |= registration_cmds[i]; |
571 | membarrier_state &= ~states[i]; |
572 | } |
573 | } |
574 | WARN_ON_ONCE(membarrier_state != 0); |
575 | return registrations_mask; |
576 | } |
577 | |
578 | /** |
579 | * sys_membarrier - issue memory barriers on a set of threads |
580 | * @cmd: Takes command values defined in enum membarrier_cmd. |
581 | * @flags: Currently needs to be 0 for all commands other than |
582 | * MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: in the latter |
583 | * case it can be MEMBARRIER_CMD_FLAG_CPU, indicating that @cpu_id |
584 | * contains the CPU on which to interrupt (= restart) |
585 | * the RSEQ critical section. |
586 | * @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, indicates the cpu on which |
587 | * RSEQ CS should be interrupted (@cmd must be |
588 | * MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ). |
589 | * |
590 | * If this system call is not implemented, -ENOSYS is returned. If the |
591 | * command specified does not exist, not available on the running |
592 | * kernel, or if the command argument is invalid, this system call |
593 | * returns -EINVAL. For a given command, with flags argument set to 0, |
594 | * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to |
595 | * always return the same value until reboot. In addition, it can return |
596 | * -ENOMEM if there is not enough memory available to perform the system |
597 | * call. |
598 | * |
599 | * All memory accesses performed in program order from each targeted thread |
600 | * is guaranteed to be ordered with respect to sys_membarrier(). If we use |
601 | * the semantic "barrier()" to represent a compiler barrier forcing memory |
602 | * accesses to be performed in program order across the barrier, and |
603 | * smp_mb() to represent explicit memory barriers forcing full memory |
604 | * ordering across the barrier, we have the following ordering table for |
605 | * each pair of barrier(), sys_membarrier() and smp_mb(): |
606 | * |
607 | * The pair ordering is detailed as (O: ordered, X: not ordered): |
608 | * |
609 | * barrier() smp_mb() sys_membarrier() |
610 | * barrier() X X O |
611 | * smp_mb() X O O |
612 | * sys_membarrier() O O O |
613 | */ |
614 | SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id) |
615 | { |
616 | switch (cmd) { |
617 | case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: |
618 | if (unlikely(flags && flags != MEMBARRIER_CMD_FLAG_CPU)) |
619 | return -EINVAL; |
620 | break; |
621 | default: |
622 | if (unlikely(flags)) |
623 | return -EINVAL; |
624 | } |
625 | |
626 | if (!(flags & MEMBARRIER_CMD_FLAG_CPU)) |
627 | cpu_id = -1; |
628 | |
629 | switch (cmd) { |
630 | case MEMBARRIER_CMD_QUERY: |
631 | { |
632 | int cmd_mask = MEMBARRIER_CMD_BITMASK; |
633 | |
634 | if (tick_nohz_full_enabled()) |
635 | cmd_mask &= ~MEMBARRIER_CMD_GLOBAL; |
636 | return cmd_mask; |
637 | } |
638 | case MEMBARRIER_CMD_GLOBAL: |
639 | /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */ |
640 | if (tick_nohz_full_enabled()) |
641 | return -EINVAL; |
642 | if (num_online_cpus() > 1) |
643 | synchronize_rcu(); |
644 | return 0; |
645 | case MEMBARRIER_CMD_GLOBAL_EXPEDITED: |
646 | return membarrier_global_expedited(); |
647 | case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED: |
648 | return membarrier_register_global_expedited(); |
649 | case MEMBARRIER_CMD_PRIVATE_EXPEDITED: |
650 | return membarrier_private_expedited(flags: 0, cpu_id); |
651 | case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED: |
652 | return membarrier_register_private_expedited(flags: 0); |
653 | case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE: |
654 | return membarrier_private_expedited(flags: MEMBARRIER_FLAG_SYNC_CORE, cpu_id); |
655 | case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE: |
656 | return membarrier_register_private_expedited(flags: MEMBARRIER_FLAG_SYNC_CORE); |
657 | case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: |
658 | return membarrier_private_expedited(flags: MEMBARRIER_FLAG_RSEQ, cpu_id); |
659 | case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ: |
660 | return membarrier_register_private_expedited(flags: MEMBARRIER_FLAG_RSEQ); |
661 | case MEMBARRIER_CMD_GET_REGISTRATIONS: |
662 | return membarrier_get_registrations(); |
663 | default: |
664 | return -EINVAL; |
665 | } |
666 | } |
667 | |