linux-kernel - Re: [PATCH] block: replace __getblk_slow misfix by grow_dev

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Date:	Wed, 22 Aug 2012 10:12:59 +0100
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <jaxboe@...ionio.com>,
	Torsten Hilbrich <torsten.hilbrich@...unet.com>,
	Josh Boyer <jwboyer@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: replace __getblk_slow misfix by grow_dev_page fix

On Tue, Aug 21, 2012 at 06:33:45PM -0700, Hugh Dickins wrote:
> Jeff,
> 
> Your commit 91f68c89d8f3 ("block: fix infinite loop in __getblk_slow"),
> already gone into 3.* stable, is not good.  Could you and your testers
> please give this alternative a try - I think it should work, and have
> started it on a few days' memory load on 3.5, but not tried your case.

I'll try your patch later today, but the test is very simple:

- Create a 1024 byte empty (all zeroes) partition and then try to mount it.

Failure was that the mount command would go into an infinite loop
using 100% CPU.  Success is that it gives an error.

More about it here including a very simple libguestfs script to
reproduce it:

  https://bugzilla.redhat.com/show_bug.cgi?id=835019#c0

and a virtual disk image that also demonstrates the problem without
needing anything except a VM running the test kernel:

  https://bugzilla.redhat.com/show_bug.cgi?id=835019#c1

Rich.

-- 
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