Patch "Btrfs: fix log tree corruption when fs mounted with -o discard" has been added to the 3.14-stable tree

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

Btrfs: fix log tree corruption when fs mounted with -o discard

to the 3.14-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:
btrfs-fix-log-tree-corruption-when-fs-mounted-with-o-discard.patch
and it can be found in the queue-3.14 subdirectory.

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

From: Filipe Manana <[email protected]>
Date: Mon, 23 Mar 2015 14:07:40 +0000
Subject: Btrfs: fix log tree corruption when fs mounted with -o discard

From: Filipe Manana <[email protected]>

commit dcc82f4783ad91d4ab654f89f37ae9291cdc846a upstream.

While committing a transaction we free the log roots before we write the new super block. Freeing the log roots implies marking the disk location of every node/leaf (metadata extent) as pinned before the new super block is written. This is to prevent the disk location of log metadata extents from being reused before the new super block is written, otherwise we would have a corrupted log tree if before the new super block is written a crash/reboot happens and the location of any log tree metadata extent ended up being reused and rewritten.

Even though we pinned the log tree's metadata extents, we were issuing a discard against them if the fs was mounted with the -o discard option, resulting in corruption of the log tree if a crash/reboot happened before writing the new super block - the next time the fs was mounted, during the log replay process we would find nodes/leafs of the log btree with a content full of zeroes, causing the process to fail and require the use of the tool btrfs-zero-log to wipeout the log tree (and all data previously fsynced becoming lost forever).

Fix this by not doing a discard when pinning an extent. The discard will be done later when it's safe (after the new super block is committed) at extent-tree.c:btrfs_finish_extent_commit().

---
 fs/btrfs/extent-tree.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

@@ -6645,12 +6645,11 @@ static int __btrfs_free_reserved_extent(
 		return -ENOSPC;
 	}
 
-	if (btrfs_test_opt(root, DISCARD))
-		ret = btrfs_discard_extent(root, start, len, NULL);
-
 	if (pin)
 		pin_down_extent(root, cache, start, len, 1);
 	else {
+		if (btrfs_test_opt(root, DISCARD))
+			ret = btrfs_discard_extent(root, start, len, NULL);
 		btrfs_add_free_space(cache, start, len);
 		btrfs_update_reserved_bytes(cache, len, RESERVE_FREE);
 	}

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

queue-3.14/btrfs-fix-log-tree-corruption-when-fs-mounted-with-o-discard.patch queue-3.14/btrfs-fix-inode-eviction-infinite-loop-after-extent_same-ioctl.patch queue-3.14/btrfs-fix-inode-eviction-infinite-loop-after-cloning-into-it.patch