Message-ID: <3EE7D5F2.1070508@cyberone.com.au>
Date: Thu, 12 Jun 2003 11:22:58 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: Robert Love <rml@tech9.net>
CC: Andrew Morton <akpm@digeo.com>, bos@serpentine.com,
       linux-kernel@vger.kernel.org
Subject: Re: [patch] as-iosched divide by zero fix
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Robert Love wrote:

>On Wed, 2003-06-11 at 17:24, Andrew Morton wrote:
>
>
>>Do you know what the actual oops is?
>>
>
>I got it all figured out now.
>
>It is a divide by zero in update_write_batch() called from
>as_completed_request().
>
>
>>Odd that starting the X server triggers it.  Be interesting if your patch
>>fixes things for Brian.
>>
>
>I reproduced it without X.
>
>The divide by zero is on line 959 with the divide by 'write_time'. It
>can obviously be zero (see line 950). The divide by 'batch' on line 953
>seems safe.
>
>The correct patch is below.
>

Probably put in the other check to be on the safe side.
And can the check be if (!write_time || (batch / write_time > 2)

>
>
>Most important question: why are only some of us seeing this?
>

It would occur if a write batch didn't take any jiffies, which
isn't very likely. The HZ=100 change probbly brought it out.
Thanks guys.


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