[PATCH] xfs: fix stale inode flush avoidance

[PATCH] xfs: fix stale inode flush avoidance

[Dave Chinner]

When reclaiming stale inodes, we need to guarantee that inodes are
unpinned before returning with a "clean" status. If we don't we can
reclaim inodes that are pinned, leading to use after free in the
transaction subsystem as transactions complete.

Signed-off-by: Dave Chinner <david@fromorbit.com>
---
 fs/xfs/xfs_inode.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 391d36b..ef77fd8 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2842,13 +2842,9 @@ xfs_iflush(
 
 	/*
 	 * If the inode isn't dirty, then just release the inode flush lock and
-	 * do nothing. Treat stale inodes the same; we cannot rely on the
-	 * backing buffer remaining stale in cache for the remaining life of
-	 * the stale inode and so xfs_itobp() below may give us a buffer that
-	 * no longer contains inodes below. Doing this stale check here also
-	 * avoids forcing the log on pinned, stale inodes.
+	 * do nothing.
 	 */
-	if (xfs_inode_clean(ip) || xfs_iflags_test(ip, XFS_ISTALE)) {
+	if (xfs_inode_clean(ip)) {
 		xfs_ifunlock(ip);
 		return 0;
 	}
@@ -2872,6 +2868,19 @@ xfs_iflush(
 	xfs_iunpin_wait(ip);
 
 	/*
+	 * For stale inodes we cannot rely on the backing buffer remaining
+	 * stale in cache for the remaining life of the stale inode and so
+	 * xfs_itobp() below may give us a buffer that no longer contains
+	 * inodes below. We have to check this after ensuring the inode is
+	 * unpinned so that it is safe to reclaim the stale inode after the
+	 * flush call.
+	 */
+	if (xfs_iflags_test(ip, XFS_ISTALE)) {
+		xfs_ifunlock(ip);
+		return 0;
+	}
+
+	/*
 	 * This may have been unpinned because the filesystem is shutting
 	 * down forcibly. If that's the case we must not write this inode
 	 * to disk, because the log record didn't make it to disk!
-- 
1.6.5

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Re: [PATCH] xfs: fix stale inode flush avoidance

[Christoph Hellwig]

On Mon, Jan 11, 2010 at 10:45:21PM +1100, Dave Chinner wrote:
> When reclaiming stale inodes, we need to guarantee that inodes are
> unpinned before returning with a "clean" status. If we don't we can
> reclaim inodes that are pinned, leading to use after free in the
> transaction subsystem as transactions complete.

Looks good.  Per discussion this morning the clean check might not be
good enough for delwri buffers either, but as let's leave that for the
more throughout redo of the inode buffer flushing.

Reviewed-by: Christoph Hellwig <hch@lst.de>

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