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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: "Dan Williams" <dan.j.williams@xxxxxxxxx>
Date: Mon, 22 Jan 2007 18:44:11 -0700
Cc: "Chuck Ebbert" <cebbert@xxxxxxxxxx>, "Justin Piszcz" <jpiszcz@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
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On 1/22/07, Neil Brown <neilb@xxxxxxx> 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.

Coming from an ARM background I am not yet versed in the inner
workings of kmap_atomic, but if you have time for a question I am
curious as to why spin_lock(&sh->lock)  is not sufficient pre-emption
protection for copy_data() in this case?

NeilBrown

Regards,
Dan


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