From: Dave Chinner <david@fromorbit.com>
To: Brian Foster <bfoster@redhat.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 1/7] xfs: zero length symlinks are not valid
Date: Wed, 21 Nov 2018 08:19:18 +1100 [thread overview]
Message-ID: <20181120211918.GR19305@dastard> (raw)
In-Reply-To: <20181120134439.GA47711@bfoster>
On Tue, Nov 20, 2018 at 08:44:39AM -0500, Brian Foster wrote:
> On Tue, Nov 20, 2018 at 08:04:53AM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > A log recovery failure has been reproduced where a symlink inode has
> > a zero length in extent form. It was caused by a shutdown during a
> > combined fstress+fsmark workload.
> >
> > The underlying problem is the issue in xfs_inactive_symlink(): the
> > inode is unlocked between the symlink inactivation/truncation and
> > the inode being freed. This opens a window for the inode to be
> > written to disk before it xfs_ifree() removes it from the unlinked
> > list, marks it free in the inobt and zeros the mode.
> >
> > For shortform inodes, the fix is simple. xfs_ifree() clears the data
> > fork state, so there's no need to do it in xfs_inactive_symlink().
> > This means the shortform fork verifier will not see a zero length
> > data fork as it mirrors the inode size through to xfs_ifree()), and
> > hence if the inode gets written back and the fork verifiers are run
> > they will still see a fork that matches the on-disk inode size.
> >
> > For extent form (remote) symlinks, it is a little more tricky. Here
> > we explicitly set the inode size to zero, so the above race can lead
> > to zero length symlinks on disk. Because the inode is unlinked at
> > this point (i.e. on the unlinked list) and unreferenced, it can
> > never be seen again by a user. Hence when we set the inode size to
> > zeor, also change the type to S_IFREG. xfs_ifree() expects S_IFREG
> > inodes to be of zero length, and so this avoids all the problems of
> > zero length symlinks ever hitting the disk. It also avoids the
> > problem of needing to handle zero length symlink inodes in log
> > recovery to replay the extent free intents and the remaining
> > deferops to free the extents the symlink used.
> >
> > Also add a couple of asserts to warn us if zero length symlinks end
> > up in either the symlink create or inactivation paths.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
>
> Hmm, I saw this and thought this was something we had already fixed.
> Looking back, I see this was actually posted[1] months ago and there was
> a fairly nuanced discussion. On a quick skim, that appears to have
> concluded with the patch being mostly sane, but requiring a couple minor
> tweaks and commit log updates. This patch looks exactly the same to me,
> however. Hm?
Hmmm, I did all that, months ago. The code barely changed, it was
all just commit message updates. maybe I picked up the wrong version
of the patch - it had been sitting around for a while. I had even
gone back and checked the discussion before concluding that "it
doesn't need code changes" before adding it to this stack...
I'll go back and see if I can find a more recent version...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2018-11-21 7:50 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 21:04 [PATCH 0/7] xfs: various fixes for 4.20 Dave Chinner
2018-11-19 21:04 ` [PATCH 1/7] xfs: zero length symlinks are not valid Dave Chinner
2018-11-20 8:12 ` Christoph Hellwig
2018-11-20 13:44 ` Brian Foster
2018-11-20 21:19 ` Dave Chinner [this message]
2018-11-21 12:01 ` Brian Foster
2018-11-19 21:04 ` [PATCH 2/7] xfs: uncached buffer tracing needs to print bno Dave Chinner
2018-11-20 8:12 ` Christoph Hellwig
2018-11-20 22:46 ` Darrick J. Wong
2018-11-19 21:04 ` [PATCH 3/7] xfs: fix transient reference count error in xfs_buf_resubmit_failed_buffers Dave Chinner
2018-11-20 8:13 ` Christoph Hellwig
2018-11-20 22:48 ` Darrick J. Wong
2018-11-19 21:04 ` [PATCH 4/7] xfs: finobt AG reserves don't consider last AG can be a runt Dave Chinner
2018-11-20 8:14 ` Christoph Hellwig
2018-11-20 22:49 ` Darrick J. Wong
2018-11-19 21:04 ` [PATCH 5/7] xfs: extent shifting doesn't fully invalidate page cache Dave Chinner
2018-11-20 8:18 ` Christoph Hellwig
2018-11-20 22:53 ` Darrick J. Wong
2018-11-19 21:04 ` [PATCH 6/7] xfs: don't ENOSPC on writeback when punching holes Dave Chinner
2018-11-20 8:20 ` Christoph Hellwig
2018-11-20 9:50 ` Dave Chinner
2018-11-20 16:28 ` Christoph Hellwig
2018-11-20 21:00 ` Dave Chinner
2018-11-21 18:09 ` Darrick J. Wong
2018-11-22 2:31 ` Dave Chinner
2018-11-19 21:04 ` [PATCH 7/7] xfs: flush removing page cache in xfs_reflink_remap_prep Dave Chinner
2018-11-20 8:32 ` Christoph Hellwig
2018-11-20 22:56 ` Darrick J. Wong
2018-11-20 6:36 ` [PATCH 8/7] xfs: delalloc -> unwritten COW fork allocation can go wrong Dave Chinner
2018-11-20 13:45 ` Brian Foster
2018-11-20 16:33 ` Christoph Hellwig
2018-11-20 21:08 ` Dave Chinner
2018-11-20 16:32 ` Christoph Hellwig
2018-11-20 22:58 ` Darrick J. Wong
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