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Subject[76/80] hung_task: fix false positive during vfork
3.1-stable review patch.  If anyone has any objections, please let me know.

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Content-Length: 1649
Lines: 48

From: Mandeep Singh Baines <msb@chromium.org>

commit f9fab10bbd768b0e5254e53a4a8477a94bfc4b96 upstream.

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 <msb@chromium.org>
Reported-by: Sasha Levin <levinsasha928@gmail.com>
LKML-Reference: <1325344394.28904.43.camel@lappy>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/hung_task.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -74,11 +74,17 @@ static void check_hung_task(struct task_

/*
* 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) {



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