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1/*
2 * Copyright (C) 2010-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 *
4 * membarrier system call
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 */
16#include "sched.h"
17
18/*
19 * Bitmask made from a "or" of all commands within enum membarrier_cmd,
20 * except MEMBARRIER_CMD_QUERY.
21 */
22#ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
23#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
24 (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \
25 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE)
26#else
27#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0
28#endif
29
30#define MEMBARRIER_CMD_BITMASK \
31 (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \
32 | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \
33 | MEMBARRIER_CMD_PRIVATE_EXPEDITED \
34 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \
35 | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
36
37static void ipi_mb(void *info)
38{
39 smp_mb(); /* IPIs should be serializing but paranoid. */
40}
41
42static int membarrier_global_expedited(void)
43{
44 int cpu;
45 bool fallback = false;
46 cpumask_var_t tmpmask;
47
48 if (num_online_cpus() == 1)
49 return 0;
50
51 /*
52 * Matches memory barriers around rq->curr modification in
53 * scheduler.
54 */
55 smp_mb(); /* system call entry is not a mb. */
56
57 /*
58 * Expedited membarrier commands guarantee that they won't
59 * block, hence the GFP_NOWAIT allocation flag and fallback
60 * implementation.
61 */
62 if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
63 /* Fallback for OOM. */
64 fallback = true;
65 }
66
67 cpus_read_lock();
68 for_each_online_cpu(cpu) {
69 struct task_struct *p;
70
71 /*
72 * Skipping the current CPU is OK even through we can be
73 * migrated at any point. The current CPU, at the point
74 * where we read raw_smp_processor_id(), is ensured to
75 * be in program order with respect to the caller
76 * thread. Therefore, we can skip this CPU from the
77 * iteration.
78 */
79 if (cpu == raw_smp_processor_id())
80 continue;
81
82 rcu_read_lock();
83 p = task_rcu_dereference(&cpu_rq(cpu)->curr);
84 if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
85 MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
86 if (!fallback)
87 __cpumask_set_cpu(cpu, tmpmask);
88 else
89 smp_call_function_single(cpu, ipi_mb, NULL, 1);
90 }
91 rcu_read_unlock();
92 }
93 if (!fallback) {
94 preempt_disable();
95 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
96 preempt_enable();
97 free_cpumask_var(tmpmask);
98 }
99 cpus_read_unlock();
100
101 /*
102 * Memory barrier on the caller thread _after_ we finished
103 * waiting for the last IPI. Matches memory barriers around
104 * rq->curr modification in scheduler.
105 */
106 smp_mb(); /* exit from system call is not a mb */
107 return 0;
108}
109
110static int membarrier_private_expedited(int flags)
111{
112 int cpu;
113 bool fallback = false;
114 cpumask_var_t tmpmask;
115
116 if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
117 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
118 return -EINVAL;
119 if (!(atomic_read(¤t->mm->membarrier_state) &
120 MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
121 return -EPERM;
122 } else {
123 if (!(atomic_read(¤t->mm->membarrier_state) &
124 MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
125 return -EPERM;
126 }
127
128 if (num_online_cpus() == 1)
129 return 0;
130
131 /*
132 * Matches memory barriers around rq->curr modification in
133 * scheduler.
134 */
135 smp_mb(); /* system call entry is not a mb. */
136
137 /*
138 * Expedited membarrier commands guarantee that they won't
139 * block, hence the GFP_NOWAIT allocation flag and fallback
140 * implementation.
141 */
142 if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
143 /* Fallback for OOM. */
144 fallback = true;
145 }
146
147 cpus_read_lock();
148 for_each_online_cpu(cpu) {
149 struct task_struct *p;
150
151 /*
152 * Skipping the current CPU is OK even through we can be
153 * migrated at any point. The current CPU, at the point
154 * where we read raw_smp_processor_id(), is ensured to
155 * be in program order with respect to the caller
156 * thread. Therefore, we can skip this CPU from the
157 * iteration.
158 */
159 if (cpu == raw_smp_processor_id())
160 continue;
161 rcu_read_lock();
162 p = task_rcu_dereference(&cpu_rq(cpu)->curr);
163 if (p && p->mm == current->mm) {
164 if (!fallback)
165 __cpumask_set_cpu(cpu, tmpmask);
166 else
167 smp_call_function_single(cpu, ipi_mb, NULL, 1);
168 }
169 rcu_read_unlock();
170 }
171 if (!fallback) {
172 preempt_disable();
173 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
174 preempt_enable();
175 free_cpumask_var(tmpmask);
176 }
177 cpus_read_unlock();
178
179 /*
180 * Memory barrier on the caller thread _after_ we finished
181 * waiting for the last IPI. Matches memory barriers around
182 * rq->curr modification in scheduler.
183 */
184 smp_mb(); /* exit from system call is not a mb */
185
186 return 0;
187}
188
189static int membarrier_register_global_expedited(void)
190{
191 struct task_struct *p = current;
192 struct mm_struct *mm = p->mm;
193
194 if (atomic_read(&mm->membarrier_state) &
195 MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
196 return 0;
197 atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
198 if (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) {
199 /*
200 * For single mm user, single threaded process, we can
201 * simply issue a memory barrier after setting
202 * MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that
203 * no memory access following registration is reordered
204 * before registration.
205 */
206 smp_mb();
207 } else {
208 /*
209 * For multi-mm user threads, we need to ensure all
210 * future scheduler executions will observe the new
211 * thread flag state for this mm.
212 */
213 synchronize_sched();
214 }
215 atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
216 &mm->membarrier_state);
217
218 return 0;
219}
220
221static int membarrier_register_private_expedited(int flags)
222{
223 struct task_struct *p = current;
224 struct mm_struct *mm = p->mm;
225 int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY;
226
227 if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
228 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
229 return -EINVAL;
230 state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
231 }
232
233 /*
234 * We need to consider threads belonging to different thread
235 * groups, which use the same mm. (CLONE_VM but not
236 * CLONE_THREAD).
237 */
238 if (atomic_read(&mm->membarrier_state) & state)
239 return 0;
240 atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
241 if (flags & MEMBARRIER_FLAG_SYNC_CORE)
242 atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE,
243 &mm->membarrier_state);
244 if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) {
245 /*
246 * Ensure all future scheduler executions will observe the
247 * new thread flag state for this process.
248 */
249 synchronize_sched();
250 }
251 atomic_or(state, &mm->membarrier_state);
252
253 return 0;
254}
255
256/**
257 * sys_membarrier - issue memory barriers on a set of threads
258 * @cmd: Takes command values defined in enum membarrier_cmd.
259 * @flags: Currently needs to be 0. For future extensions.
260 *
261 * If this system call is not implemented, -ENOSYS is returned. If the
262 * command specified does not exist, not available on the running
263 * kernel, or if the command argument is invalid, this system call
264 * returns -EINVAL. For a given command, with flags argument set to 0,
265 * this system call is guaranteed to always return the same value until
266 * reboot.
267 *
268 * All memory accesses performed in program order from each targeted thread
269 * is guaranteed to be ordered with respect to sys_membarrier(). If we use
270 * the semantic "barrier()" to represent a compiler barrier forcing memory
271 * accesses to be performed in program order across the barrier, and
272 * smp_mb() to represent explicit memory barriers forcing full memory
273 * ordering across the barrier, we have the following ordering table for
274 * each pair of barrier(), sys_membarrier() and smp_mb():
275 *
276 * The pair ordering is detailed as (O: ordered, X: not ordered):
277 *
278 * barrier() smp_mb() sys_membarrier()
279 * barrier() X X O
280 * smp_mb() X O O
281 * sys_membarrier() O O O
282 */
283SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
284{
285 if (unlikely(flags))
286 return -EINVAL;
287 switch (cmd) {
288 case MEMBARRIER_CMD_QUERY:
289 {
290 int cmd_mask = MEMBARRIER_CMD_BITMASK;
291
292 if (tick_nohz_full_enabled())
293 cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
294 return cmd_mask;
295 }
296 case MEMBARRIER_CMD_GLOBAL:
297 /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
298 if (tick_nohz_full_enabled())
299 return -EINVAL;
300 if (num_online_cpus() > 1)
301 synchronize_sched();
302 return 0;
303 case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
304 return membarrier_global_expedited();
305 case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
306 return membarrier_register_global_expedited();
307 case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
308 return membarrier_private_expedited(0);
309 case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
310 return membarrier_register_private_expedited(0);
311 case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
312 return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
313 case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
314 return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
315 default:
316 return -EINVAL;
317 }
318}
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#include "sched.h"
8
9/*
10 * Bitmask made from a "or" of all commands within enum membarrier_cmd,
11 * except MEMBARRIER_CMD_QUERY.
12 */
13#ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
14#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
15 (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \
16 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE)
17#else
18#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0
19#endif
20
21#define MEMBARRIER_CMD_BITMASK \
22 (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \
23 | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \
24 | MEMBARRIER_CMD_PRIVATE_EXPEDITED \
25 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \
26 | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
27
28static void ipi_mb(void *info)
29{
30 smp_mb(); /* IPIs should be serializing but paranoid. */
31}
32
33static void ipi_sync_rq_state(void *info)
34{
35 struct mm_struct *mm = (struct mm_struct *) info;
36
37 if (current->mm != mm)
38 return;
39 this_cpu_write(runqueues.membarrier_state,
40 atomic_read(&mm->membarrier_state));
41 /*
42 * Issue a memory barrier after setting
43 * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to
44 * guarantee that no memory access following registration is reordered
45 * before registration.
46 */
47 smp_mb();
48}
49
50void membarrier_exec_mmap(struct mm_struct *mm)
51{
52 /*
53 * Issue a memory barrier before clearing membarrier_state to
54 * guarantee that no memory access prior to exec is reordered after
55 * clearing this state.
56 */
57 smp_mb();
58 atomic_set(&mm->membarrier_state, 0);
59 /*
60 * Keep the runqueue membarrier_state in sync with this mm
61 * membarrier_state.
62 */
63 this_cpu_write(runqueues.membarrier_state, 0);
64}
65
66static int membarrier_global_expedited(void)
67{
68 int cpu;
69 cpumask_var_t tmpmask;
70
71 if (num_online_cpus() == 1)
72 return 0;
73
74 /*
75 * Matches memory barriers around rq->curr modification in
76 * scheduler.
77 */
78 smp_mb(); /* system call entry is not a mb. */
79
80 if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
81 return -ENOMEM;
82
83 cpus_read_lock();
84 rcu_read_lock();
85 for_each_online_cpu(cpu) {
86 struct task_struct *p;
87
88 /*
89 * Skipping the current CPU is OK even through we can be
90 * migrated at any point. The current CPU, at the point
91 * where we read raw_smp_processor_id(), is ensured to
92 * be in program order with respect to the caller
93 * thread. Therefore, we can skip this CPU from the
94 * iteration.
95 */
96 if (cpu == raw_smp_processor_id())
97 continue;
98
99 if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) &
100 MEMBARRIER_STATE_GLOBAL_EXPEDITED))
101 continue;
102
103 /*
104 * Skip the CPU if it runs a kernel thread. The scheduler
105 * leaves the prior task mm in place as an optimization when
106 * scheduling a kthread.
107 */
108 p = rcu_dereference(cpu_rq(cpu)->curr);
109 if (p->flags & PF_KTHREAD)
110 continue;
111
112 __cpumask_set_cpu(cpu, tmpmask);
113 }
114 rcu_read_unlock();
115
116 preempt_disable();
117 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
118 preempt_enable();
119
120 free_cpumask_var(tmpmask);
121 cpus_read_unlock();
122
123 /*
124 * Memory barrier on the caller thread _after_ we finished
125 * waiting for the last IPI. Matches memory barriers around
126 * rq->curr modification in scheduler.
127 */
128 smp_mb(); /* exit from system call is not a mb */
129 return 0;
130}
131
132static int membarrier_private_expedited(int flags)
133{
134 int cpu;
135 cpumask_var_t tmpmask;
136 struct mm_struct *mm = current->mm;
137
138 if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
139 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
140 return -EINVAL;
141 if (!(atomic_read(&mm->membarrier_state) &
142 MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
143 return -EPERM;
144 } else {
145 if (!(atomic_read(&mm->membarrier_state) &
146 MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
147 return -EPERM;
148 }
149
150 if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1)
151 return 0;
152
153 /*
154 * Matches memory barriers around rq->curr modification in
155 * scheduler.
156 */
157 smp_mb(); /* system call entry is not a mb. */
158
159 if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
160 return -ENOMEM;
161
162 cpus_read_lock();
163 rcu_read_lock();
164 for_each_online_cpu(cpu) {
165 struct task_struct *p;
166
167 /*
168 * Skipping the current CPU is OK even through we can be
169 * migrated at any point. The current CPU, at the point
170 * where we read raw_smp_processor_id(), is ensured to
171 * be in program order with respect to the caller
172 * thread. Therefore, we can skip this CPU from the
173 * iteration.
174 */
175 if (cpu == raw_smp_processor_id())
176 continue;
177 p = rcu_dereference(cpu_rq(cpu)->curr);
178 if (p && p->mm == mm)
179 __cpumask_set_cpu(cpu, tmpmask);
180 }
181 rcu_read_unlock();
182
183 preempt_disable();
184 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
185 preempt_enable();
186
187 free_cpumask_var(tmpmask);
188 cpus_read_unlock();
189
190 /*
191 * Memory barrier on the caller thread _after_ we finished
192 * waiting for the last IPI. Matches memory barriers around
193 * rq->curr modification in scheduler.
194 */
195 smp_mb(); /* exit from system call is not a mb */
196
197 return 0;
198}
199
200static int sync_runqueues_membarrier_state(struct mm_struct *mm)
201{
202 int membarrier_state = atomic_read(&mm->membarrier_state);
203 cpumask_var_t tmpmask;
204 int cpu;
205
206 if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
207 this_cpu_write(runqueues.membarrier_state, membarrier_state);
208
209 /*
210 * For single mm user, we can simply issue a memory barrier
211 * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the
212 * mm and in the current runqueue to guarantee that no memory
213 * access following registration is reordered before
214 * registration.
215 */
216 smp_mb();
217 return 0;
218 }
219
220 if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
221 return -ENOMEM;
222
223 /*
224 * For mm with multiple users, we need to ensure all future
225 * scheduler executions will observe @mm's new membarrier
226 * state.
227 */
228 synchronize_rcu();
229
230 /*
231 * For each cpu runqueue, if the task's mm match @mm, ensure that all
232 * @mm's membarrier state set bits are also set in in the runqueue's
233 * membarrier state. This ensures that a runqueue scheduling
234 * between threads which are users of @mm has its membarrier state
235 * updated.
236 */
237 cpus_read_lock();
238 rcu_read_lock();
239 for_each_online_cpu(cpu) {
240 struct rq *rq = cpu_rq(cpu);
241 struct task_struct *p;
242
243 p = rcu_dereference(rq->curr);
244 if (p && p->mm == mm)
245 __cpumask_set_cpu(cpu, tmpmask);
246 }
247 rcu_read_unlock();
248
249 preempt_disable();
250 smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);
251 preempt_enable();
252
253 free_cpumask_var(tmpmask);
254 cpus_read_unlock();
255
256 return 0;
257}
258
259static int membarrier_register_global_expedited(void)
260{
261 struct task_struct *p = current;
262 struct mm_struct *mm = p->mm;
263 int ret;
264
265 if (atomic_read(&mm->membarrier_state) &
266 MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
267 return 0;
268 atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
269 ret = sync_runqueues_membarrier_state(mm);
270 if (ret)
271 return ret;
272 atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
273 &mm->membarrier_state);
274
275 return 0;
276}
277
278static int membarrier_register_private_expedited(int flags)
279{
280 struct task_struct *p = current;
281 struct mm_struct *mm = p->mm;
282 int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
283 set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED,
284 ret;
285
286 if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
287 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
288 return -EINVAL;
289 ready_state =
290 MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
291 }
292
293 /*
294 * We need to consider threads belonging to different thread
295 * groups, which use the same mm. (CLONE_VM but not
296 * CLONE_THREAD).
297 */
298 if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state)
299 return 0;
300 if (flags & MEMBARRIER_FLAG_SYNC_CORE)
301 set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE;
302 atomic_or(set_state, &mm->membarrier_state);
303 ret = sync_runqueues_membarrier_state(mm);
304 if (ret)
305 return ret;
306 atomic_or(ready_state, &mm->membarrier_state);
307
308 return 0;
309}
310
311/**
312 * sys_membarrier - issue memory barriers on a set of threads
313 * @cmd: Takes command values defined in enum membarrier_cmd.
314 * @flags: Currently needs to be 0. For future extensions.
315 *
316 * If this system call is not implemented, -ENOSYS is returned. If the
317 * command specified does not exist, not available on the running
318 * kernel, or if the command argument is invalid, this system call
319 * returns -EINVAL. For a given command, with flags argument set to 0,
320 * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to
321 * always return the same value until reboot. In addition, it can return
322 * -ENOMEM if there is not enough memory available to perform the system
323 * call.
324 *
325 * All memory accesses performed in program order from each targeted thread
326 * is guaranteed to be ordered with respect to sys_membarrier(). If we use
327 * the semantic "barrier()" to represent a compiler barrier forcing memory
328 * accesses to be performed in program order across the barrier, and
329 * smp_mb() to represent explicit memory barriers forcing full memory
330 * ordering across the barrier, we have the following ordering table for
331 * each pair of barrier(), sys_membarrier() and smp_mb():
332 *
333 * The pair ordering is detailed as (O: ordered, X: not ordered):
334 *
335 * barrier() smp_mb() sys_membarrier()
336 * barrier() X X O
337 * smp_mb() X O O
338 * sys_membarrier() O O O
339 */
340SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
341{
342 if (unlikely(flags))
343 return -EINVAL;
344 switch (cmd) {
345 case MEMBARRIER_CMD_QUERY:
346 {
347 int cmd_mask = MEMBARRIER_CMD_BITMASK;
348
349 if (tick_nohz_full_enabled())
350 cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
351 return cmd_mask;
352 }
353 case MEMBARRIER_CMD_GLOBAL:
354 /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
355 if (tick_nohz_full_enabled())
356 return -EINVAL;
357 if (num_online_cpus() > 1)
358 synchronize_rcu();
359 return 0;
360 case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
361 return membarrier_global_expedited();
362 case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
363 return membarrier_register_global_expedited();
364 case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
365 return membarrier_private_expedited(0);
366 case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
367 return membarrier_register_private_expedited(0);
368 case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
369 return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
370 case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
371 return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
372 default:
373 return -EINVAL;
374 }
375}