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| author | Peter Zijlstra <peterz@infradead.org> | 2015-10-06 15:36:17 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-12-04 12:26:42 +0300 |
| commit | b75a22531588e77aa8c2daf228c9723916ae2cd0 (patch) | |
| tree | 410014f762b59ea5dd46e4f58b1f1a4728a01c4a | |
| parent | 2541117b0cf79977fa11a0d6e17d61010677bd7b (diff) | |
| download | linux-b75a22531588e77aa8c2daf228c9723916ae2cd0.tar.xz | |
sched/core: Better document the try_to_wake_up() barriers
Explain how the control dependency and smp_rmb() end up providing
ACQUIRE semantics and pair with smp_store_release() in
finish_lock_switch().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | kernel/sched/core.c | 8 | ||||
| -rw-r--r-- | kernel/sched/sched.h | 3 |
2 files changed, 10 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index eee4ee655db2..b64f163d512c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1953,7 +1953,13 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) while (p->on_cpu) cpu_relax(); /* - * Pairs with the smp_wmb() in finish_lock_switch(). + * Combined with the control dependency above, we have an effective + * smp_load_acquire() without the need for full barriers. + * + * Pairs with the smp_store_release() in finish_lock_switch(). + * + * This ensures that tasks getting woken will be fully ordered against + * their previous state and preserve Program Order. */ smp_rmb(); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index efd3bfc7e347..b242775bf670 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1073,6 +1073,9 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev) * We must ensure this doesn't happen until the switch is completely * finished. * + * In particular, the load of prev->state in finish_task_switch() must + * happen before this. + * * Pairs with the control dependency and rmb in try_to_wake_up(). */ smp_store_release(&prev->on_cpu, 0); |