tree e7dacbb7f370e0d7c515ed743a2c5b5179a1de5e
parent 6cd8dedcdd8e8de01391a7cf25f0b2afeb24f8f4
author Tejun Heo <tj@kernel.org> 1321907544 -0800
committer Tejun Heo <tj@kernel.org> 1321907544 -0800

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

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>