linux-kernel - Re: Re: cfq-iosched.c: panic in cfq_dispatch

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Date:	Tue, 22 Mar 2011 11:39:27 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Lina Lu <lulina_nuaa@...mail.com>
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: Re: cfq-iosched.c: panic in cfq_dispatch_requests

On Tue, Mar 22, 2011 at 11:32:47PM +0800, Lina Lu wrote:
> On 2011-03-21 22:08:19, Vivek Goyal wrote:
> >On Sun, Mar 20, 2011 at 03:23:23PM +0800, Lina Lu wrote:
> >> Hi Vivek,
> >> 
> >> I did some test with blkio weight policy these days. The kernel panic 
> >> once in a while. 
> >> 	
> >> From the calltrace, It 's in func cfq_dispatch_requests(+0x058D).
> >> And I caught a divide by zero error with system monitor tools.
> >
> >Hi Lina,
> >
> >Can you please paste the full backtrace here.
> >
> >> 	
> >> The panic happens when I first set 100 weight to two IO pids, then 
> >> change the weight to 200, and begin to perform IO. The kernel panic
> >> accurately when the IO begin.
> >
> >So you notice this only if weights are changed otherwise not?
> 
> Hi Vivek
> 
> Thanks for this patch! I did objdump and find place that divide by zero.
> It's in cfq_group_slice function, the st->total_weight is zero in my issue.
> As described in the patch, this is because I change the weight when the
> group on service tree. 

Ok, so this patch did solve the issue you are facing? 

Thanks
Vivek
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