Freezer: Fix a race during freezing of TASK_STOPPED tasks (8cfe400c) · Commits · 戴 / test

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>

kernel/freezer.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -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() 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 {

kernel/power/process.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -64,6 +64,12 @@ static int try_to_freeze_tasks(bool sig_only)
		* perturb a task in TASK_STOPPED or TASK_TRACED.
		* It is "frozen enough". If the task does wake
		* up, it will immediately call try_to_freeze.
		*
		* Because freeze_task() goes through p's
		* scheduler lock after setting TIF_FREEZE, it's
		* guaranteed that either we see TASK_RUNNING or
		* try_to_stop() after schedule() in ptrace/signal
		* stop sees TIF_FREEZE.
		*/
		if (!task_is_stopped_or_traced(p) &&
		!freezer_should_skip(p))

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