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22e4ebb9 MD |
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 | */ | |
325ea10c | 16 | #include "sched.h" |
22e4ebb9 MD |
17 | |
18 | /* | |
19 | * Bitmask made from a "or" of all commands within enum membarrier_cmd, | |
20 | * except MEMBARRIER_CMD_QUERY. | |
21 | */ | |
70216e18 | 22 | #ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE |
97fb7a0a IM |
23 | #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \ |
24 | (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \ | |
70216e18 MD |
25 | | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE) |
26 | #else | |
27 | #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0 | |
28 | #endif | |
29 | ||
97fb7a0a IM |
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 \ | |
70216e18 | 35 | | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK) |
22e4ebb9 MD |
36 | |
37 | static void ipi_mb(void *info) | |
38 | { | |
39 | smp_mb(); /* IPIs should be serializing but paranoid. */ | |
40 | } | |
41 | ||
c5f58bd5 MD |
42 | static 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; | |
97fb7a0a | 81 | |
c5f58bd5 MD |
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 | ||
70216e18 | 110 | static int membarrier_private_expedited(int flags) |
22e4ebb9 MD |
111 | { |
112 | int cpu; | |
113 | bool fallback = false; | |
114 | cpumask_var_t tmpmask; | |
115 | ||
70216e18 MD |
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 | } | |
a961e409 | 127 | |
22e4ebb9 | 128 | if (num_online_cpus() == 1) |
a961e409 | 129 | return 0; |
22e4ebb9 MD |
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) { | |
54167607 | 172 | preempt_disable(); |
22e4ebb9 | 173 | smp_call_function_many(tmpmask, ipi_mb, NULL, 1); |
54167607 | 174 | preempt_enable(); |
22e4ebb9 MD |
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 */ | |
97fb7a0a | 185 | |
a961e409 MD |
186 | return 0; |
187 | } | |
188 | ||
c5f58bd5 MD |
189 | static 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 | */ | |
c9a863bb | 213 | synchronize_rcu(); |
c5f58bd5 MD |
214 | } |
215 | atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY, | |
216 | &mm->membarrier_state); | |
97fb7a0a | 217 | |
c5f58bd5 MD |
218 | return 0; |
219 | } | |
220 | ||
70216e18 | 221 | static int membarrier_register_private_expedited(int flags) |
a961e409 MD |
222 | { |
223 | struct task_struct *p = current; | |
224 | struct mm_struct *mm = p->mm; | |
70216e18 MD |
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 | } | |
a961e409 MD |
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 | */ | |
70216e18 | 238 | if (atomic_read(&mm->membarrier_state) & state) |
c5f58bd5 | 239 | return 0; |
3ccfebed | 240 | atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state); |
70216e18 MD |
241 | if (flags & MEMBARRIER_FLAG_SYNC_CORE) |
242 | atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE, | |
243 | &mm->membarrier_state); | |
3ccfebed MD |
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 | */ | |
c9a863bb | 249 | synchronize_rcu(); |
3ccfebed | 250 | } |
70216e18 | 251 | atomic_or(state, &mm->membarrier_state); |
97fb7a0a | 252 | |
c5f58bd5 | 253 | return 0; |
22e4ebb9 MD |
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 | */ | |
283 | SYSCALL_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()) | |
c5f58bd5 | 293 | cmd_mask &= ~MEMBARRIER_CMD_GLOBAL; |
22e4ebb9 MD |
294 | return cmd_mask; |
295 | } | |
c5f58bd5 MD |
296 | case MEMBARRIER_CMD_GLOBAL: |
297 | /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */ | |
22e4ebb9 MD |
298 | if (tick_nohz_full_enabled()) |
299 | return -EINVAL; | |
300 | if (num_online_cpus() > 1) | |
78d125d3 | 301 | synchronize_rcu(); |
22e4ebb9 | 302 | return 0; |
c5f58bd5 MD |
303 | case MEMBARRIER_CMD_GLOBAL_EXPEDITED: |
304 | return membarrier_global_expedited(); | |
305 | case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED: | |
306 | return membarrier_register_global_expedited(); | |
22e4ebb9 | 307 | case MEMBARRIER_CMD_PRIVATE_EXPEDITED: |
70216e18 | 308 | return membarrier_private_expedited(0); |
a961e409 | 309 | case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED: |
70216e18 MD |
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); | |
22e4ebb9 MD |
315 | default: |
316 | return -EINVAL; | |
317 | } | |
318 | } |