From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH 1/5] xfs: take the ilock around xfs_bmapi_read in xfs_zero_remaining_bytes
Date: Fri, 6 Dec 2013 07:31:15 +1100 [thread overview]
Message-ID: <20131205203115.GA29897@dastard> (raw)
In-Reply-To: <20131205155951.199565525@bombadil.infradead.org>
On Thu, Dec 05, 2013 at 07:58:31AM -0800, Christoph Hellwig wrote:
> Signed-off-by: Christoph Hellwig <hch@lst.de>
>
> Index: xfs/fs/xfs/xfs_bmap_util.c
> ===================================================================
> --- xfs.orig/fs/xfs/xfs_bmap_util.c 2013-12-05 11:37:57.791685284 +0100
> +++ xfs/fs/xfs/xfs_bmap_util.c 2013-12-05 11:39:43.599683113 +0100
> @@ -1147,6 +1147,7 @@ xfs_zero_remaining_bytes(
> xfs_mount_t *mp = ip->i_mount;
> int nimap;
> int error = 0;
> + uint lock_mode;
>
> /*
> * Avoid doing I/O beyond eof - it's not necessary
> @@ -1159,11 +1160,15 @@ xfs_zero_remaining_bytes(
> if (endoff > XFS_ISIZE(ip))
> endoff = XFS_ISIZE(ip);
>
> + lock_mode = xfs_ilock_map_shared(ip);
> +
> bp = xfs_buf_get_uncached(XFS_IS_REALTIME_INODE(ip) ?
> mp->m_rtdev_targp : mp->m_ddev_targp,
> BTOBB(mp->m_sb.sb_blocksize), 0);
This now holds the ilock over data IO, which is not allowed to be
done as data IO completion can require the ilock to be taken. Yes,
the code specifically avoids all these problems, but the general
rule is that ilock is only held over metadata IO operations, not
data IO. If we need data IO serialisation, then we use the iolock.
So, while this protects the extent tree, it also violates other
long-standing conventions for locking. Given that the code is
special, I'mnot opposed to making a special rule for this one
function, but it needs to be commented as to why this is a valid
thing to do in this function....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2013-12-05 20:31 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-05 15:58 [PATCH 0/5] extent list locking fixes Christoph Hellwig
2013-12-05 15:58 ` [PATCH 1/5] xfs: take the ilock around xfs_bmapi_read in xfs_zero_remaining_bytes Christoph Hellwig
2013-12-05 19:38 ` Ben Myers
2013-12-05 20:31 ` Dave Chinner [this message]
2013-12-05 20:37 ` Ben Myers
2013-12-05 20:40 ` Christoph Hellwig
2013-12-05 15:58 ` [PATCH 2/5] xfs: use xfs_ilock_map_shared in xfs_qm_dqtobp Christoph Hellwig
2013-12-05 19:46 ` Ben Myers
2013-12-05 20:41 ` Dave Chinner
2013-12-05 20:53 ` Christoph Hellwig
2013-12-05 21:03 ` Dave Chinner
2013-12-05 15:58 ` [PATCH 3/5] xfs: use xfs_ilock_map_shared in xfs_qm_dqiterate Christoph Hellwig
2013-12-05 19:48 ` Ben Myers
2013-12-05 20:45 ` Dave Chinner
2013-12-05 15:58 ` [PATCH 4/5] xfs: use xfs_ilock_map_shared in xfs_attr_get Christoph Hellwig
2013-12-05 19:57 ` Ben Myers
2013-12-05 20:59 ` Dave Chinner
2013-12-05 21:01 ` Christoph Hellwig
2013-12-05 21:05 ` Dave Chinner
2013-12-05 21:10 ` Christoph Hellwig
2013-12-05 21:17 ` Dave Chinner
2013-12-05 15:58 ` [PATCH 5/5] xfs: assert that we hold the ilock for extent map access Christoph Hellwig
2013-12-05 20:11 ` Ben Myers
2013-12-05 21:10 ` Dave Chinner
2013-12-05 21:22 ` Christoph Hellwig
2013-12-05 21:40 ` Dave Chinner
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