linux-kernel - [PATCH] hung_task: fix false positive during vfork

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Message-Id: <1325630473-27477-1-git-send-email-msb@chromium.org>
Date:	Tue,  3 Jan 2012 14:41:13 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mandeep Singh Baines <msb@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Kacur <jkacur@...hat.com>
Subject: [PATCH] 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 <msb@...omium.org>
Reported-by: Sasha Levin <levinsasha928@...il.com>
LKML-Reference: <1325344394.28904.43.camel@...py>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: John Kacur <jkacur@...hat.com>
---
 kernel/hung_task.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 8b1748d..2e48ec0 100644
--- 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) {
-- 
1.7.3.1

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