linux-kernel - Re: [BUG -rt] Double OOPs - thread_info free race / printk recursive lock

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Date:	Fri, 4 Aug 2006 14:10:11 -0700
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [BUG -rt] Double OOPs - thread_info free race / printk recursive lock

On Fri, Aug 04, 2006 at 10:43:05AM -0700, Darren Hart wrote:
> We've seen very rarely over the last few months, on various -rt kernels.  The 
> latest reproduction is on 2.6.16-rt22 (+some minor fixups).  Analysis of the 
> vmcore produced by kdump suggests two problems: 
> 1) An invalid pointer dereference in cache_flusharray() which causes the page
> fault.  

My guess is that this is after some bogus stuff going on after the real event.

> 2) Then printk calls kmalloc when trying to print the oops, which grabs a
> recursive lock and prints a different oops.  

Can't say for sure, but this sounds a lot like the problem I've been dealing
with in free_task(). The stack trace is pretty contorted and it's been difficult
to unwind it in any meaningful manner, although I'm making progress.  Writing
some tools to deal with this now.

bill

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