From: Dave Chinner <david@fromorbit.com>
To: ira.weiny@intel.com
Cc: linux-kernel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Dan Williams <dan.j.williams@intel.com>,
Christoph Hellwig <hch@lst.de>,
"Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 06/12] fs/xfs: Check if the inode supports DAX under lock
Date: Tue, 11 Feb 2020 17:16:39 +1100 [thread overview]
Message-ID: <20200211061639.GH10776@dread.disaster.area> (raw)
In-Reply-To: <20200208193445.27421-7-ira.weiny@intel.com>
On Sat, Feb 08, 2020 at 11:34:39AM -0800, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> One of the checks for an inode supporting DAX is if the inode is
> reflinked. During a non-DAX to DAX state change we could race with
> the file being reflinked and end up with a reflinked file being in DAX
> state.
>
> Prevent this race by checking for DAX support under the MMAP_LOCK.
The on disk inode flags are protected by the XFS_ILOCK, not the
MMAP_LOCK. i.e. the MMAPLOCK provides data access serialisation, not
metadata modification serialisation.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> fs/xfs/xfs_ioctl.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index da1eb2bdb386..4ff402fd6636 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1194,10 +1194,6 @@ xfs_ioctl_setattr_dax_invalidate(
>
> *join_flags = 0;
>
> - if ((fa->fsx_xflags & FS_XFLAG_DAX) == FS_XFLAG_DAX &&
> - !xfs_inode_supports_dax(ip))
> - return -EINVAL;
> -
> /* If the DAX state is not changing, we have nothing to do here. */
> if ((fa->fsx_xflags & FS_XFLAG_DAX) &&
> (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
> @@ -1211,6 +1207,13 @@ xfs_ioctl_setattr_dax_invalidate(
>
> /* lock, flush and invalidate mapping in preparation for flag change */
> xfs_ilock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
> +
> + if ((fa->fsx_xflags & FS_XFLAG_DAX) == FS_XFLAG_DAX &&
> + !xfs_inode_supports_dax(ip)) {
> + error = -EINVAL;
> + goto out_unlock;
> + }
Yes, you might be able to get away with reflink vs dax flag
serialisation on the inode flag modification, but it is not correct and
leaves a landmine for future inode flag modifications that are done
without holding either the MMAP or IOLOCK.
e.g. concurrent calls to xfs_ioctl_setattr() setting/clearing flags
other than the on disk DAX flag are all serialised by the ILOCK_EXCL
and will no be serialised against this DAX check. Hence if there are
other flags that we add in future that affect the result of
xfs_inode_supports_dax(), this code will not be correctly
serialised.
This raciness in checking the DAX flags is the reason that
xfs_ioctl_setattr_xflags() redoes all the reflink vs dax checks once
it's called under the XFS_ILOCK_EXCL during the actual change
transaction....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2020-02-11 6:16 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-08 19:34 [PATCH v3 00/12] Enable per-file/directory DAX operations V3 ira.weiny
2020-02-08 19:34 ` [PATCH v3 01/12] fs/stat: Define DAX statx attribute ira.weiny
2020-02-08 19:34 ` [PATCH v3 02/12] fs/xfs: Isolate the physical DAX flag from effective ira.weiny
2020-02-08 19:34 ` [PATCH v3 03/12] fs/xfs: Separate functionality of xfs_inode_supports_dax() ira.weiny
2020-02-11 5:47 ` Dave Chinner
2020-02-11 16:13 ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 04/12] fs/xfs: Clean up DAX support check ira.weiny
2020-02-11 5:57 ` Dave Chinner
2020-02-11 16:28 ` Ira Weiny
2020-02-11 20:38 ` Dave Chinner
2020-02-08 19:34 ` [PATCH v3 05/12] fs: remove unneeded IS_DAX() check ira.weiny
2020-02-11 5:34 ` Dave Chinner
2020-02-11 16:38 ` Ira Weiny
2020-02-11 20:41 ` Dave Chinner
2020-02-12 16:04 ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 06/12] fs/xfs: Check if the inode supports DAX under lock ira.weiny
2020-02-11 6:16 ` Dave Chinner [this message]
2020-02-11 17:55 ` Ira Weiny
2020-02-11 20:42 ` Dave Chinner
2020-02-12 16:10 ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 07/12] fs: Add locking for a dynamic DAX state ira.weiny
2020-02-11 8:00 ` Dave Chinner
2020-02-11 20:14 ` Ira Weiny
2020-02-11 20:59 ` Dan Williams
2020-02-11 21:49 ` Dave Chinner
2020-02-12 6:31 ` Darrick J. Wong
2020-02-08 19:34 ` [PATCH v3 08/12] fs/xfs: Clarify lockdep dependency for xfs_isilocked() ira.weiny
2020-02-08 19:34 ` [PATCH v3 09/12] fs/xfs: Add write DAX lock to xfs layer ira.weiny
2020-02-08 19:34 ` [PATCH v3 10/12] fs: Prevent DAX state change if file is mmap'ed ira.weiny
2020-02-08 19:34 ` [PATCH v3 11/12] fs/xfs: Clean up locking in dax invalidate ira.weiny
2020-02-08 19:34 ` [PATCH v3 12/12] fs/xfs: Allow toggle of effective DAX flag ira.weiny
2020-02-10 15:15 ` [PATCH v3 00/12] Enable per-file/directory DAX operations V3 Jeff Moyer
2020-02-11 20:17 ` Ira Weiny
2020-02-12 19:49 ` Jeff Moyer
2020-02-13 19:01 ` Ira Weiny
2020-02-13 19:05 ` Ira Weiny
2020-02-13 19:58 ` Darrick J. Wong
2020-02-13 23:29 ` Ira Weiny
2020-02-14 0:16 ` Dan Williams
2020-02-14 20:06 ` Ira Weiny
2020-02-14 21:23 ` Jeff Moyer
2020-02-14 21:58 ` Ira Weiny
2020-02-14 22:06 ` Jeff Moyer
2020-02-14 22:58 ` Jeff Moyer
2020-02-14 23:03 ` Jeff Moyer
2020-02-18 2:35 ` Ira Weiny
2020-02-18 14:22 ` Jeff Moyer
2020-02-18 23:54 ` Ira Weiny
2020-02-20 16:20 ` Ira Weiny
2020-02-20 16:30 ` Darrick J. Wong
2020-02-20 16:49 ` Ira Weiny
2020-02-20 17:00 ` Darrick J. Wong
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