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freezer: use dedicated lock instead of task_lock() + memory barrier

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Freezer synchronization is needlessly complicated - it's by no means a
hot path and the priority is staying unintrusive and safe.  This patch
makes it simply use a dedicated lock instead of piggy-backing on
task_lock() and playing with memory barriers.

On the failure path of try_to_freeze_tasks(), locking is moved from it
to cancel_freezing().  This makes the frozen() test racy but the race
here is a non-issue as the warning is printed for tasks which failed
to enter frozen for 20 seconds and race on PF_FROZEN at the last
moment doesn't change anything.

This simplifies freezer implementation and eases further changes
including some race fixes.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2011-11-21 12:32:24 -08:00
parent 6cd8dedcdd
commit 0c9af09262
2 changed files with 36 additions and 48 deletions
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2
kernel/power/process.c
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@ -118,11 +118,9 @@ static int try_to_freeze_tasks(bool sig_only)
read_lock(&tasklist_lock);
do_each_thread(g, p) {
task_lock(p);
if (!wakeup && freezing(p) && !freezer_should_skip(p))
sched_show_task(p);
cancel_freezing(p);
task_unlock(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
} else {