linux-kernel - Re: [PATCH] Re: Bio device too big | kernel BUG at mm/filemap.c:537!

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Message-ID: <17866.19962.601479.638730@notabene.brown>
Date:	Thu, 8 Feb 2007 09:08:58 +1100
From:	Neil Brown <neilb@...e.de>
To:	"Kai" <epimetreus@...tmail.fm>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Re: Bio device too big | kernel BUG at mm/filemap.c:537!

On Wednesday February 7, epimetreus@...tmail.fm wrote:
> 
> On Wed, 7 Feb 2007 10:26:56 +1100, "Neil Brown" <neilb@...e.de> said:
> > On Tuesday February 6, neilb@...e.de wrote:
> > > 
> > > This patch should fix the worst of the offences, but I'd like to
> > > experiment and think a bit more before I submit it to stable.
> > > And probably test it too - as yet I have only compile and brain
> > > tested.
> > 
> > Ok, I've experimented and tested and now I know what was causing the
> > double-unlock.
> > 
> > The following patch is suitable for 2.6.20.1 and mainline.  There is
> > room for a bit more improvement, but only for performance, not
> > correctness.  I'll look into that later.
> > 
> > Thanks,
> > NeilBrown
> 
> I figure I should test this on my hardware, but since the RAID array
> resynched itself when I rebooted back into an earlier kernel version,
> I'm guessing it means this bug introduced some corruption into the
> array, when it occurred, so I'd like some pointers on how I can test it
> out without compromising my data.

This bug should not introduce any data corruption.
It causes some read requests to get a failure from the device, which
will cause raid5 to remove the device from the array (Though the data
will still be intact).
On restart a resync will put everything back as it was.

It is quite possible (this happened to me in my testing) for several
devices to get these errors and for several or even all of these
device to get failed.  However even in this case the data is still
intact and "mdadm --assemble --force ..." will put everything back
together.

So there should be no risk of data corruption.

NeilBrown
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