Messages in this thread |  | | Date | Fri, 26 Oct 2012 10:52:58 -0700 | | From | Tejun Heo <> | | Subject | Re: [PATCH v2 1/1] freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() |
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On Fri, Oct 26, 2012 at 07:46:06PM +0200, Oleg Nesterov wrote: > try_to_freeze_tasks() and cgroup_freezer rely on scheduler locks > to ensure that a task doing STOPPED/TRACED -> RUNNING transition > can't escape freezing. This mostly works, but ptrace_stop() does > not necessarily call schedule(), it can change task->state back to > RUNNING and check freezing() without any lock/barrier in between. > > We could add the necessary barrier, but this patch changes > ptrace_stop() and do_signal_stop() to use freezable_schedule(). > This fixes the race, freezer_count() and freezer_should_skip() > carefully avoid the race. > > And this simplifies the code, try_to_freeze_tasks/update_if_frozen > no longer need to use task_is_stopped_or_traced() checks with the > non trivial assumptions. We can rely on the mechanism which was > specially designed to mark the sleeping task as "frozen enough". > > v2: As Tejun pointed out, we can also change get_signal_to_deliver() > and move try_to_freeze() up before 'relock' label. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Looks good to me. :)
Acked-by: Tejun Heo <tj@kernel.org>
Rafael, sorry that this one doesn't have pm cc'd but can you please pick up this one too?
Thanks a lot.
-- tejun
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