From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org,
Amir Goldstein <amir73il@gmail.com>,
Boaz Harrosh <boaz@plexistor.com>,
linux-fsdevel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 3/3] xfs: Fix stale data exposure when readahead races with hole punch
Date: Wed, 18 Sep 2019 09:07:12 -0700 [thread overview]
Message-ID: <20190918160712.GV2229799@magnolia> (raw)
In-Reply-To: <20190918123123.GC31891@quack2.suse.cz>
On Wed, Sep 18, 2019 at 02:31:24PM +0200, Jan Kara wrote:
> On Fri 30-08-19 17:24:49, Jan Kara wrote:
> > On Thu 29-08-19 08:52:04, Darrick J. Wong wrote:
> > > On Thu, Aug 29, 2019 at 03:10:34PM +0200, Jan Kara wrote:
> > > > Hole puching currently evicts pages from page cache and then goes on to
> > > > remove blocks from the inode. This happens under both XFS_IOLOCK_EXCL
> > > > and XFS_MMAPLOCK_EXCL which provides appropriate serialization with
> > > > racing reads or page faults. However there is currently nothing that
> > > > prevents readahead triggered by fadvise() or madvise() from racing with
> > > > the hole punch and instantiating page cache page after hole punching has
> > > > evicted page cache in xfs_flush_unmap_range() but before it has removed
> > > > blocks from the inode. This page cache page will be mapping soon to be
> > > > freed block and that can lead to returning stale data to userspace or
> > > > even filesystem corruption.
> > > >
> > > > Fix the problem by protecting handling of readahead requests by
> > > > XFS_IOLOCK_SHARED similarly as we protect reads.
> > > >
> > > > CC: stable@vger.kernel.org
> > > > Link: https://lore.kernel.org/linux-fsdevel/CAOQ4uxjQNmxqmtA_VbYW0Su9rKRk2zobJmahcyeaEVOFKVQ5dw@mail.gmail.com/
> > > > Reported-by: Amir Goldstein <amir73il@gmail.com>
> > > > Signed-off-by: Jan Kara <jack@suse.cz>
> > >
> > > Is there a test on xfstests to demonstrate this race?
> >
> > No, but I can try to create one.
>
> I was experimenting with this but I could not reproduce the issue in my
> test VM without inserting artificial delay at appropriate place... So I
> don't think there's much point in the fstest for this.
<shrug> We've added debugging knobs to XFS that inject delays to
demonstrate race conditions that are hard to reproduce, but OTOH it's
more fun to have a generic/ test that you can use to convince the other
fs maintainers to take your patches. :)
--D
> Honza
>
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
next prev parent reply other threads:[~2019-09-18 16:07 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-29 13:10 [PATCH 0/3 v2] xfs: Fix races between readahead and hole punching Jan Kara
2019-08-29 13:10 ` [PATCH 1/3] mm: Handle MADV_WILLNEED through vfs_fadvise() Jan Kara
2019-08-29 15:49 ` Darrick J. Wong
2019-08-29 13:10 ` [PATCH 2/3] fs: Export generic_fadvise() Jan Kara
2019-08-29 13:10 ` [PATCH 3/3] xfs: Fix stale data exposure when readahead races with hole punch Jan Kara
2019-08-29 15:52 ` Darrick J. Wong
2019-08-30 15:24 ` Jan Kara
2019-08-30 16:02 ` Darrick J. Wong
2019-09-18 12:31 ` Jan Kara
2019-09-18 16:07 ` Darrick J. Wong [this message]
2019-09-23 12:33 ` Boaz Harrosh
2019-09-24 15:23 ` Jan Kara
2019-09-24 15:45 ` Boaz Harrosh
2020-01-17 10:50 ` [PATCH 0/3 v2] xfs: Fix races between readahead and hole punching Amir Goldstein
2020-01-19 8:35 ` Amir Goldstein
2020-01-20 11:47 ` Jan Kara
2020-01-20 12:03 ` Jan Kara
2020-01-20 13:54 ` Amir Goldstein
2020-01-20 16:58 ` Jan Kara
-- strict thread matches above, loose matches on Subject: below --
2019-07-11 14:00 [PATCH 0/3] " Jan Kara
2019-07-11 14:00 ` [PATCH 3/3] xfs: Fix stale data exposure when readahead races with hole punch Jan Kara
2019-07-11 15:28 ` Amir Goldstein
2019-07-11 15:49 ` Darrick J. Wong
2019-07-12 12:00 ` Jan Kara
2019-07-12 17:56 ` Darrick J. Wong
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