Commit cf2592f5 authored Feb 10, 2009 by Frederic Weisbecker Committed by Ingo Molnar Feb 11, 2009

softlockup: ensure the task has been switched out once



When we check if a task has been switched out since the last scan, we might
have a race condition on the following scenario:

- the task is freshly created and scheduled

- it puts its state to TASK_UNINTERRUPTIBLE and is not yet switched out

- check_hung_task() scans this task and will report a false positive because
  t->nvcsw + t->nivcsw == t->last_switch_count == 0

Add a check for such cases.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 17406b82

kernel/hung_task.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -72,7 +72,13 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
		{
		unsigned long switch_count = t->nvcsw + t->nivcsw;

		if (t->flags & PF_FROZEN)
		/*
		* Ensure the task is not frozen.
		* Also, when a freshly created task is scheduled once, changes
		* its state to TASK_UNINTERRUPTIBLE without having ever been
		* switched out once, it musn't be checked.
		*/
		if (unlikely(t->flags & PF_FROZEN \|\| !switch_count))
		return;

		if (switch_count != t->last_switch_count) {