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 <o...@redhat.com>
Looks good to me. :) Acked-by: Tejun Heo <t...@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
