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

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Message-ID: <20080912025458.GF27054@hoblitt.com>
Date:	Thu, 11 Sep 2008 16:54:58 -1000
From:	j_kernel@...litt.com
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bugme-new] [Bug 11543] New: kernel panic: softlockup in
	tick_periodic() ???

On Thu, Sep 11, 2008 at 05:02:58PM -0700, Andrew Morton wrote:
> Is this a regression?  Was 2.6.26 OK, for example?

It might be a regression. ;) The last build we were running on this
hardware was 2.6.24.2 and NMI watchdog support was not enabled.  We were
however experiencing random deadlocks, which I had been attributing to
problems with forcedeth.c (which causes the NIC to totally crap out
but not deadlock the machine) but I am now of the mind that there are
multiple problems with distinct failure modes.

> I can't work out who called panic(), nor why.

One more data point.  We booted this kernel on 14 machines this morning
and only one has had this panic thus far...

> 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().
> 
> Something like this:
> 
> --- a/include/linux/debug_locks.h~a
> +++ a/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;						\
> _
> 
> might prevent the debugging code from preventing us from finding bugs :(

Do you want me to give that patch a try or sit tight for a bit?

-J

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