linux-kernel - Re: [Bugme-new] [Bug 11543] New: kernel panic: softlockup in tick

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Message-ID: <20080912091308.GA10305@elte.hu>
Date:	Fri, 12 Sep 2008 11:13:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	bugme-daemon@...zilla.kernel.org, j_kernel@...litt.com
Subject: Re: [Bugme-new] [Bug 11543] New: kernel panic: softlockup in
	tick_periodic() ???


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> I can't work out who called panic(), nor why.
> 
> The panic code called the kexec code which called mutex_trylock() 
> which called spin_lock_mutex() which then stupidly went and blurted a 
> load of debug stuff because of in_interrupt().

agreed - applied your fix in the form below to tip/master - thanks 
Andrew.

J, you might want to try tip/master, it includes all known fixes for 
this area and this debug improvement as well. You can pick it up via:

  http://people.redhat.com/mingo/tip.git/README

	Ingo

---------->
>From 53b9d87f41a3d8838210ad7cdef02d814817ce85 Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@...ux-foundation.org>
Date: Thu, 11 Sep 2008 17:02:58 -0700
Subject: [PATCH] lock debug: sit tight when we are already in a panic

in:

  > http://bugzilla.kernel.org/show_bug.cgi?id=11543

The panic code called the kexec code which called mutex_trylock() which
called spin_lock_mutex() which then stupidly went and blurted a load of
debug stuff because of in_interrupt().

Keep the lock debug code from escallating an already crappy situation.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/debug_locks.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/debug_locks.h b/include/linux/debug_locks.h
index 4aaa4af..096476f 100644
--- a/include/linux/debug_locks.h
+++ b/include/linux/debug_locks.h
@@ -17,7 +17,7 @@ extern int debug_locks_off(void);
 ({									\
 	int __ret = 0;							\
 									\
-	if (unlikely(c)) {						\
+	if (!oops_in_progress && unlikely(c)) {				\
 		if (debug_locks_off() && !debug_locks_silent)		\
 			WARN_ON(1);					\
 		__ret = 1;						\
--
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