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

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Date:	Tue, 23 Jan 2007 08:59:36 +1100
From:	Neil Brown <neilb@...e.de>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	Justin Piszcz <jpiszcz@...idpixels.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	xfs@....sgi.com
Subject: Re: Kernel 2.6.19.2 New RAID 5 Bug (oops when writing Samba -> RAID5)

On Monday January 22, cebbert@...hat.com 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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