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authorTejun Heo <tj@kernel.org>2010-11-26 23:07:27 +0100
committerRafael J. Wysocki <rjw@sisk.pl>2010-12-24 15:02:40 +0100
commit8cfe400ca54fd1ed96f962bea5f7e20b09b6d69f (patch)
tree393f1eb68d2497b04778c2e062fc4e1450df33eb /kernel/freezer.c
parent133f1128b2bf178a1976b17c54bd14ce6feb90bf (diff)
downloadvexpress-lsk-8cfe400ca54fd1ed96f962bea5f7e20b09b6d69f.tar.gz
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 <tj@kernel.org> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Diffstat (limited to 'kernel/freezer.c')
-rw-r--r--kernel/freezer.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c
index bd1d42b17cb..66ecd2ead21 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 {