treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157
[sfrench/cifs-2.6.git] / kernel / sched / membarrier.c
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
28 static void ipi_mb(void *info)
29 {
30         smp_mb();       /* IPIs should be serializing but paranoid. */
31 }
32
33 static int membarrier_global_expedited(void)
34 {
35         int cpu;
36         bool fallback = false;
37         cpumask_var_t tmpmask;
38
39         if (num_online_cpus() == 1)
40                 return 0;
41
42         /*
43          * Matches memory barriers around rq->curr modification in
44          * scheduler.
45          */
46         smp_mb();       /* system call entry is not a mb. */
47
48         /*
49          * Expedited membarrier commands guarantee that they won't
50          * block, hence the GFP_NOWAIT allocation flag and fallback
51          * implementation.
52          */
53         if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
54                 /* Fallback for OOM. */
55                 fallback = true;
56         }
57
58         cpus_read_lock();
59         for_each_online_cpu(cpu) {
60                 struct task_struct *p;
61
62                 /*
63                  * Skipping the current CPU is OK even through we can be
64                  * migrated at any point. The current CPU, at the point
65                  * where we read raw_smp_processor_id(), is ensured to
66                  * be in program order with respect to the caller
67                  * thread. Therefore, we can skip this CPU from the
68                  * iteration.
69                  */
70                 if (cpu == raw_smp_processor_id())
71                         continue;
72
73                 rcu_read_lock();
74                 p = task_rcu_dereference(&cpu_rq(cpu)->curr);
75                 if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
76                                    MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
77                         if (!fallback)
78                                 __cpumask_set_cpu(cpu, tmpmask);
79                         else
80                                 smp_call_function_single(cpu, ipi_mb, NULL, 1);
81                 }
82                 rcu_read_unlock();
83         }
84         if (!fallback) {
85                 preempt_disable();
86                 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
87                 preempt_enable();
88                 free_cpumask_var(tmpmask);
89         }
90         cpus_read_unlock();
91
92         /*
93          * Memory barrier on the caller thread _after_ we finished
94          * waiting for the last IPI. Matches memory barriers around
95          * rq->curr modification in scheduler.
96          */
97         smp_mb();       /* exit from system call is not a mb */
98         return 0;
99 }
100
101 static int membarrier_private_expedited(int flags)
102 {
103         int cpu;
104         bool fallback = false;
105         cpumask_var_t tmpmask;
106
107         if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
108                 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
109                         return -EINVAL;
110                 if (!(atomic_read(&current->mm->membarrier_state) &
111                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
112                         return -EPERM;
113         } else {
114                 if (!(atomic_read(&current->mm->membarrier_state) &
115                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
116                         return -EPERM;
117         }
118
119         if (num_online_cpus() == 1)
120                 return 0;
121
122         /*
123          * Matches memory barriers around rq->curr modification in
124          * scheduler.
125          */
126         smp_mb();       /* system call entry is not a mb. */
127
128         /*
129          * Expedited membarrier commands guarantee that they won't
130          * block, hence the GFP_NOWAIT allocation flag and fallback
131          * implementation.
132          */
133         if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
134                 /* Fallback for OOM. */
135                 fallback = true;
136         }
137
138         cpus_read_lock();
139         for_each_online_cpu(cpu) {
140                 struct task_struct *p;
141
142                 /*
143                  * Skipping the current CPU is OK even through we can be
144                  * migrated at any point. The current CPU, at the point
145                  * where we read raw_smp_processor_id(), is ensured to
146                  * be in program order with respect to the caller
147                  * thread. Therefore, we can skip this CPU from the
148                  * iteration.
149                  */
150                 if (cpu == raw_smp_processor_id())
151                         continue;
152                 rcu_read_lock();
153                 p = task_rcu_dereference(&cpu_rq(cpu)->curr);
154                 if (p && p->mm == current->mm) {
155                         if (!fallback)
156                                 __cpumask_set_cpu(cpu, tmpmask);
157                         else
158                                 smp_call_function_single(cpu, ipi_mb, NULL, 1);
159                 }
160                 rcu_read_unlock();
161         }
162         if (!fallback) {
163                 preempt_disable();
164                 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
165                 preempt_enable();
166                 free_cpumask_var(tmpmask);
167         }
168         cpus_read_unlock();
169
170         /*
171          * Memory barrier on the caller thread _after_ we finished
172          * waiting for the last IPI. Matches memory barriers around
173          * rq->curr modification in scheduler.
174          */
175         smp_mb();       /* exit from system call is not a mb */
176
177         return 0;
178 }
179
180 static int membarrier_register_global_expedited(void)
181 {
182         struct task_struct *p = current;
183         struct mm_struct *mm = p->mm;
184
185         if (atomic_read(&mm->membarrier_state) &
186             MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
187                 return 0;
188         atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
189         if (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) {
190                 /*
191                  * For single mm user, single threaded process, we can
192                  * simply issue a memory barrier after setting
193                  * MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that
194                  * no memory access following registration is reordered
195                  * before registration.
196                  */
197                 smp_mb();
198         } else {
199                 /*
200                  * For multi-mm user threads, we need to ensure all
201                  * future scheduler executions will observe the new
202                  * thread flag state for this mm.
203                  */
204                 synchronize_rcu();
205         }
206         atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
207                   &mm->membarrier_state);
208
209         return 0;
210 }
211
212 static int membarrier_register_private_expedited(int flags)
213 {
214         struct task_struct *p = current;
215         struct mm_struct *mm = p->mm;
216         int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY;
217
218         if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
219                 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
220                         return -EINVAL;
221                 state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
222         }
223
224         /*
225          * We need to consider threads belonging to different thread
226          * groups, which use the same mm. (CLONE_VM but not
227          * CLONE_THREAD).
228          */
229         if (atomic_read(&mm->membarrier_state) & state)
230                 return 0;
231         atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
232         if (flags & MEMBARRIER_FLAG_SYNC_CORE)
233                 atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE,
234                           &mm->membarrier_state);
235         if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) {
236                 /*
237                  * Ensure all future scheduler executions will observe the
238                  * new thread flag state for this process.
239                  */
240                 synchronize_rcu();
241         }
242         atomic_or(state, &mm->membarrier_state);
243
244         return 0;
245 }
246
247 /**
248  * sys_membarrier - issue memory barriers on a set of threads
249  * @cmd:   Takes command values defined in enum membarrier_cmd.
250  * @flags: Currently needs to be 0. For future extensions.
251  *
252  * If this system call is not implemented, -ENOSYS is returned. If the
253  * command specified does not exist, not available on the running
254  * kernel, or if the command argument is invalid, this system call
255  * returns -EINVAL. For a given command, with flags argument set to 0,
256  * this system call is guaranteed to always return the same value until
257  * reboot.
258  *
259  * All memory accesses performed in program order from each targeted thread
260  * is guaranteed to be ordered with respect to sys_membarrier(). If we use
261  * the semantic "barrier()" to represent a compiler barrier forcing memory
262  * accesses to be performed in program order across the barrier, and
263  * smp_mb() to represent explicit memory barriers forcing full memory
264  * ordering across the barrier, we have the following ordering table for
265  * each pair of barrier(), sys_membarrier() and smp_mb():
266  *
267  * The pair ordering is detailed as (O: ordered, X: not ordered):
268  *
269  *                        barrier()   smp_mb() sys_membarrier()
270  *        barrier()          X           X            O
271  *        smp_mb()           X           O            O
272  *        sys_membarrier()   O           O            O
273  */
274 SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
275 {
276         if (unlikely(flags))
277                 return -EINVAL;
278         switch (cmd) {
279         case MEMBARRIER_CMD_QUERY:
280         {
281                 int cmd_mask = MEMBARRIER_CMD_BITMASK;
282
283                 if (tick_nohz_full_enabled())
284                         cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
285                 return cmd_mask;
286         }
287         case MEMBARRIER_CMD_GLOBAL:
288                 /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
289                 if (tick_nohz_full_enabled())
290                         return -EINVAL;
291                 if (num_online_cpus() > 1)
292                         synchronize_rcu();
293                 return 0;
294         case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
295                 return membarrier_global_expedited();
296         case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
297                 return membarrier_register_global_expedited();
298         case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
299                 return membarrier_private_expedited(0);
300         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
301                 return membarrier_register_private_expedited(0);
302         case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
303                 return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
304         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
305                 return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
306         default:
307                 return -EINVAL;
308         }
309 }