From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/5] iomap: FUA is wrong for DIO O_DSYNC writes into unwritten extents
Date: Mon, 19 Nov 2018 23:48:32 -0800 [thread overview]
Message-ID: <20181120074832.GA25418@infradead.org> (raw)
In-Reply-To: <20181119211742.8824-2-david@fromorbit.com>
On Tue, Nov 20, 2018 at 08:17:38AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> When we write into an unwritten extent via direct IO, we dirty
> metadata on IO completion to convert the unwritten extent to
> written. However, when we do the FUA optimisation checks, the inode
> may be clean and so we issue a FUA write into the unwritten extent.
> This means we then bypass the generic_write_sync() call after
> unwritten extent conversion has ben done and we don't force the
> modified metadata to stable storage.
>
> This violates O_DSYNC semantics. The window of exposure is a single
> IO, as the next DIO write will see the inode has dirty metadata and
> hence will not use the FUA optimisation. Calling
> generic_write_sync() after completion of the second IO will also
> sync the first write and it's metadata.
>
> Fix this by avoiding the FUA optimisation when writing to unwritten
> extents.
Ouch, yes. We can't skip the log force when converting unwritten
extent. If we really cared we could try to use FUA and only do
the log force vs needing a full device flush, but that would require
a fair amount of of work.
So this looks good:
Reviewed-by: Christoph Hellwig <hch@lst.de>
next prev parent reply other threads:[~2018-11-20 18:16 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 21:17 [PATCH 0/5] iomap: data corruption fixes and more Dave Chinner
2018-11-19 21:17 ` [PATCH 1/5] iomap: FUA is wrong for DIO O_DSYNC writes into unwritten extents Dave Chinner
2018-11-20 7:48 ` Christoph Hellwig [this message]
2018-11-20 23:00 ` Darrick J. Wong
2018-11-19 21:17 ` [PATCH 2/5] iomap: sub-block dio needs to zeroout beyond EOF Dave Chinner
2018-11-20 23:01 ` Darrick J. Wong
2018-11-19 21:17 ` [PATCH 3/5] iomap: dio data corruption and spurious errors when pipes fill Dave Chinner
2018-11-19 21:17 ` [PATCH 4/5] splice: increase pipe size in splice_direct_to_actor() Dave Chinner
2018-11-20 7:49 ` Christoph Hellwig
2018-11-20 23:02 ` Darrick J. Wong
2018-11-19 21:17 ` [PATCH 5/5] vfs: vfs_dedupe_file_range() doesn't return EOPNOTSUPP Dave Chinner
2018-11-20 7:49 ` Christoph Hellwig
2018-11-21 6:50 ` [PATCH 6/5] iomap: readpages doesn't zero page tail beyond EOF properly Dave Chinner
2018-11-21 8:27 ` [PATCH 6/5 V2] " Dave Chinner
2018-11-21 16:20 ` Darrick J. Wong
2018-11-21 16:34 ` Christoph Hellwig
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