Patch "Btrfs: fix BUG_ON in btrfs_mark_buffer_dirty" 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

Btrfs: fix BUG_ON in btrfs_mark_buffer_dirty

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:
btrfs-fix-bug_on-in-btrfs_mark_buffer_dirty.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: Liu Bo <[email protected]>
Date: Fri, 2 Sep 2016 12:35:34 -0700
Subject: Btrfs: fix BUG_ON in btrfs_mark_buffer_dirty

From: Liu Bo <[email protected]>

commit ef85b25e982b5bba1530b936e283ef129f02ab9d upstream.

This can only happen with CONFIG_BTRFS_FS_CHECK_INTEGRITY=y.

Commit 1ba98d0 ("Btrfs: detect corruption when non-root leaf has zero item") assumes that a leaf is its root when leaf->bytenr == btrfs_root_bytenr(root), however, we should not use btrfs_root_bytenr(root) since it's mainly got updated during committing transaction. So the check can fail when doing COW on this leaf while it is a root.

This changes to use "if (leaf == btrfs_root_node(root))" instead, just like how we check whether leaf is a root in __btrfs_cow_block().

---
 fs/btrfs/disk-io.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

@@ -572,13 +572,17 @@ static noinline int check_leaf(struct bt
 		 * open_ctree() some roots has not yet been set up.
 		 */
 		if (!IS_ERR_OR_NULL(check_root)) {
+			struct extent_buffer *eb;
+
+			eb = btrfs_root_node(check_root);
 			/* if leaf is the root, then it's fine */
-			if (leaf->start !=
-			    btrfs_root_bytenr(&check_root->root_item)) {
+			if (leaf != eb) {
 				CORRUPT("non-root leaf's nritems is 0",
-					leaf, root, 0);
+					leaf, check_root, 0);
+				free_extent_buffer(eb);
 				return -EIO;
 			}
+			free_extent_buffer(eb);
 		}
 		return 0;
 	}

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

queue-4.9/btrfs-fix-emptiness-check-for-dirtied-extent-buffers-at-check_leaf.patch queue-4.9/btrfs-fix-bug_on-in-btrfs_mark_buffer_dirty.patch