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Re: Kernel 2.6.19.2 New RAID 5 Bug (oops when writing Samba -> RAID5)

To: Neil Brown <neilb@xxxxxxx>
Subject: Re: Kernel 2.6.19.2 New RAID 5 Bug (oops when writing Samba -> RAID5)
From: Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>
Date: Tue, 23 Jan 2007 05:56:28 -0500 (EST)
Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <17845.13256.284461.992275@notabene.brown>
References: <Pine.LNX.4.64.0701200718290.29223@p34.internal.lan> <45B5261B.1050104@redhat.com> <17845.13256.284461.992275@notabene.brown>
Sender: xfs-bounce@xxxxxxxxxxx

On Tue, 23 Jan 2007, Neil Brown wrote:

> On Monday January 22, cebbert@xxxxxxxxxx wrote:
> > Justin Piszcz wrote:
> > > My .config is attached, please let me know if any other information is 
> > > needed and please CC (lkml) as I am not on the list, thanks!
> > >
> > > Running Kernel 2.6.19.2 on a MD RAID5 volume.  Copying files over Samba 
> > > to 
> > > the RAID5 running XFS.
> > >
> > > Any idea what happened here?
> ....
> > >   
> > Without digging too deeply, I'd say you've hit the same bug Sami Farin 
> > and others
> > have reported starting with 2.6.19: pages mapped with kmap_atomic() 
> > become unmapped
> > during memcpy() or similar operations.  Try disabling preempt -- that 
> > seems to be the
> > common factor.
> 
> That is exactly the conclusion I had just come to (a kmap_atomic page
> must be being unmapped during memcpy).  I wasn't aware that others had
> reported it - thanks for that.
> 
> Turning off CONFIG_PREEMPT certainly seems like a good idea.
> 
> NeilBrown
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Is this a bug that can or will be fixed or should I disable pre-emption on 
critical and/or server machines?

Justin.


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