netdev - Re: Linux 3.1-rc9

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Date:	Wed, 2 Nov 2011 11:28:12 -0700
From:	Simon Kirby <sim@...tway.ca>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	David Miller <davem@...emloft.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: Linux 3.1-rc9

On Wed, Nov 02, 2011 at 05:40:53PM +0100, Thomas Gleixner wrote:

> On Mon, 31 Oct 2011, Simon Kirby wrote:
> 
> > One more, again a bit different. The last few lockups have looked like
> > this. Not sure why, but we're hitting this at a few a day now. Thomas,
> > this is without your patch, but as you said, that's right before a free
> > and should print a separate lockdep warning.
> > 
> > No "huh" lines until after the trace on this one. I'll move to 3.1 with
> 
> That means that the lockdep warning hit in the same net_rx cycle
> before the leak was detected by the softirq code.
> 
> > cherry-picked b0691c8e now.
> 
> Can you please add the debug patch below and try the following:
> 
> Enable CONFIG_FUNCTION_TRACER & CONFIG_FUNCTION_GRAPH_TRACER
> 
> # cd $DEBUGFSMOUNTPOINT/tracing
> # echo sk_clone >set_ftrace_filter
> # echo function >current_tracer
> # echo 1 >options/func_stack_trace
> 
> Now wait until it reproduces (which stops the trace) and read out
> 
> # cat trace >/tmp/trace.txt
> 
> Please provide the trace file along with the lockdep splat. That
> should tell us which callchain is responsible for the spinlock
> leakage.
> Thanks,
> 
> 	tglx
> 
> --------------->
>  kernel/softirq.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> Index: linux-2.6/kernel/softirq.c
> ===================================================================
> --- linux-2.6.orig/kernel/softirq.c
> +++ linux-2.6/kernel/softirq.c
> @@ -238,6 +238,7 @@ restart:
>  			h->action(h);
>  			trace_softirq_exit(vec_nr);
>  			if (unlikely(prev_count != preempt_count())) {
> +				tracing_off();
>  				printk(KERN_ERR "huh, entered softirq %u %s %p"
>  				       "with preempt_count %08x,"
>  				       " exited with %08x?\n", vec_nr,

Ok, I'll try this. Hmm, all CPUs typically try to grab the lock fairly
quickly after it happens, which could make it difficult to cat the file.
I'll try ftrace_dump(DUMP_ALL); in there instead.

Simon-
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