Patch " xfs: handle racy AIO in xfs_reflink_end_cow" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

xfs: handle racy AIO in xfs_reflink_end_cow

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xfs-handle-racy-aio-in-xfs_reflink_end_cow.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Christoph Hellwig <[email protected]>
Date: Tue, 3 Oct 2017 08:58:33 -0700
Subject: xfs: handle racy AIO in xfs_reflink_end_cow

From: Christoph Hellwig <[email protected]>

commit e12199f85d0ad1b04ce6c425ad93cd847fe930bb upstream.

If we got two AIO writes into a COW area the second one might not have any COW extents left to convert. Handle that case gracefully instead of triggering an assert or accessing beyond the bounds of the extent list.

---
 fs/xfs/xfs_reflink.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

@@ -767,7 +767,13 @@ xfs_reflink_end_cow(
 
 	/* If there is a hole at end_fsb - 1 go to the previous extent */
 	if (eof || got.br_startoff > end_fsb) {
-		ASSERT(idx > 0);
+		/*
+		 * In case of racing, overlapping AIO writes no COW extents
+		 * might be left by the time I/O completes for the loser of
+		 * the race.  In that case we are done.
+		 */
+		if (idx <= 0)
+			goto out_cancel;
 		xfs_bmbt_get_all(xfs_iext_get_ext(ifp, --idx), &got);
 	}
 

@@ -841,6 +847,7 @@ next_extent:
 
 out_defer:
 	xfs_defer_cancel(&dfops);
+out_cancel:
 	xfs_trans_cancel(tp);
 	xfs_iunlock(ip, XFS_ILOCK_EXCL);
 out:

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/xfs-don-t-unconditionally-clear-the-reflink-flag-on-zero-block-files.patch queue-4.9/xfs-report-zeroed-or-not-correctly-in-xfs_zero_range.patch queue-4.9/xfs-handle-error-if-xfs_btree_get_bufs-fails.patch queue-4.9/xfs-update-i_size-after-unwritten-conversion-in-dio-completion.patch queue-4.9/xfs-handle-racy-aio-in-xfs_reflink_end_cow.patch queue-4.9/xfs-evict-cow-fork-extents-when-performing-finsert-fcollapse.patch queue-4.9/fs-xfs-use-ps-printk-format-for-direct-addresses.patch queue-4.9/xfs-always-swap-the-cow-forks-when-swapping-extents.patch