hung_task: fix false positive during vfork

vfork parent uninterruptibly and unkillably waits for its child to exec/exit. This wait is of unbounded length. Ignore such waits in the hung_task detector. Signed-off-by: Mandeep Singh Baines <[email protected]> Reported-by: Sasha Levin <[email protected]> LKML-Reference: <1325344394.28904.43.camel@lappy> Cc: Linus Torvalds <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Andrew Morton <[email protected]> Cc: John Kacur <[email protected]> Cc: [email protected] Signed-off-by: Linus Torvalds <[email protected]>
jadonk · Jan 4, 2012 · f9fab10 · f9fab10
1 parent 30e0532
commit f9fab10
Showing 1 changed file with 10 additions and 4 deletions.
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
@@ -74,11 +74,17 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 
 	/*
 	 * 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.
+	 * Also, skip vfork and any other user process that freezer should skip.
 	 */
-	if (unlikely(t->flags & PF_FROZEN || !switch_count))
+	if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
+	    return;
+
+	/*
+	 * 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(!switch_count))
 		return;
 
 	if (switch_count != t->last_switch_count) {