From 50fa610a3b6ba7cf91d7a92229177dfaff2b81a1 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 28 Apr 2009 15:01:38 +0100 Subject: sched: Document memory barriers implied by sleep/wake-up primitives Add a section to the memory barriers document to note the implied memory barriers of sleep primitives (set_current_state() and wrappers) and wake-up primitives (wake_up() and co.). Also extend the in-code comments on the wake_up() functions to note these implied barriers. [ Impact: add documentation ] Signed-off-by: David Howells Cc: Oleg Nesterov Cc: Linus Torvalds Cc: Andrew Morton LKML-Reference: <20090428140138.1192.94723.stgit@warthog.procyon.org.uk> Signed-off-by: Ingo Molnar --- kernel/sched.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'kernel/sched.c') diff --git a/kernel/sched.c b/kernel/sched.c index b902e587a3a..fd0c2cee3f3 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2458,6 +2458,17 @@ out: return success; } +/** + * wake_up_process - Wake up a specific process + * @p: The process to be woken up. + * + * Attempt to wake up the nominated process and move it to the set of runnable + * processes. Returns 1 if the process was woken up, 0 if it was already + * running. + * + * It may be assumed that this function implies a write memory barrier before + * changing the task state if and only if any tasks are woken up. + */ int wake_up_process(struct task_struct *p) { return try_to_wake_up(p, TASK_ALL, 0); @@ -5241,6 +5252,9 @@ void __wake_up_common(wait_queue_head_t *q, unsigned int mode, * @mode: which threads * @nr_exclusive: how many wake-one or wake-many threads to wake up * @key: is directly passed to the wakeup function + * + * It may be assumed that this function implies a write memory barrier before + * changing the task state if and only if any tasks are woken up. */ void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive, void *key) @@ -5279,6 +5293,9 @@ void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key) * with each other. This can prevent needless bouncing between CPUs. * * On UP it can prevent extra preemption. + * + * It may be assumed that this function implies a write memory barrier before + * changing the task state if and only if any tasks are woken up. */ void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode, int nr_exclusive, void *key) @@ -5315,6 +5332,9 @@ EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */ * awakened in the same order in which they were queued. * * See also complete_all(), wait_for_completion() and related routines. + * + * It may be assumed that this function implies a write memory barrier before + * changing the task state if and only if any tasks are woken up. */ void complete(struct completion *x) { @@ -5332,6 +5352,9 @@ EXPORT_SYMBOL(complete); * @x: holds the state of this particular completion * * This will wake up all threads waiting on this particular completion event. + * + * It may be assumed that this function implies a write memory barrier before + * changing the task state if and only if any tasks are woken up. */ void complete_all(struct completion *x) { -- cgit v1.2.3-18-g5258