From 5d8f72b55c275677865de670fa147ed318191d81 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 26 Oct 2012 19:46:06 +0200 Subject: freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() 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 Signed-off-by: Tejun Heo --- kernel/cgroup_freezer.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel/cgroup_freezer.c') diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index 8a92b0e52099..bedefd9a22df 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -198,8 +198,7 @@ static void update_if_frozen(struct cgroup *cgroup, struct freezer *freezer) * completion. Consider it frozen in addition to * the usual frozen condition. */ - if (!frozen(task) && !task_is_stopped_or_traced(task) && - !freezer_should_skip(task)) + if (!frozen(task) && !freezer_should_skip(task)) goto notyet; } } -- cgit v1.2.3