From 8cfe400ca54fd1ed96f962bea5f7e20b09b6d69f Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 26 Nov 2010 23:07:27 +0100 Subject: Freezer: Fix a race during freezing of TASK_STOPPED tasks After calling freeze_task(), try_to_freeze_tasks() see whether the task is stopped or traced and if so, considers it to be frozen; however, nothing guarantees that either the task being frozen sees TIF_FREEZE or the freezer sees TASK_STOPPED -> TASK_RUNNING transition. The task being frozen may wake up and not see TIF_FREEZE while the freezer fails to notice the transition and believes the task is still stopped. This patch fixes the race by making freeze_task() always go through fake_signal_wake_up() for applicable tasks. The function goes through the target task's scheduler lock and thus guarantees that either the target sees TIF_FREEZE or try_to_freeze_task() sees TASK_RUNNING. Signed-off-by: Tejun Heo Signed-off-by: Rafael J. Wysocki --- kernel/freezer.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'kernel/freezer.c') diff --git a/kernel/freezer.c b/kernel/freezer.c index bd1d42b17cb2..66ecd2ead215 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -104,8 +104,13 @@ bool freeze_task(struct task_struct *p, bool sig_only) } if (should_send_signal(p)) { - if (!signal_pending(p)) - fake_signal_wake_up(p); + fake_signal_wake_up(p); + /* + * fake_signal_wake_up() goes through p's scheduler + * lock and guarantees that TASK_STOPPED/TRACED -> + * TASK_RUNNING transition can't race with task state + * testing in try_to_freeze_tasks(). + */ } else if (sig_only) { return false; } else { -- cgit v1.2.3-59-g8ed1b