linux-ext4 - [RFC PATCH V2 06/12] fs/xfs: Check if the inode supports DAX under lock

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Date:   Fri, 10 Jan 2020 11:29:36 -0800
From:   ira.weiny@...el.com
To:     linux-kernel@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: [RFC PATCH V2 06/12] fs/xfs: Check if the inode supports DAX under lock

From: Ira Weiny <ira.weiny@...el.com>

One of the checks for an inode supporting DAX is if the inode is
reflinked.  During a non-DAX to DAX mode change we could race with
the file being reflinked and end up with a reflinked file being in DAX
mode.

Prevent this race by checking for DAX support under the MMAP_LOCK.

Signed-off-by: Ira Weiny <ira.weiny@...el.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 b5e00b67c297..bc3654fe3b5d 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1180,10 +1180,6 @@ 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))
@@ -1197,6 +1193,13 @@ 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;
+	}
+
 	error = filemap_write_and_wait(inode->i_mapping);
 	if (error)
 		goto out_unlock;
-- 
2.21.0