Patch "Btrfs: fix racy system chunk allocation when setting block group ro" has been added to the 4.0-stable tree

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

Btrfs: fix racy system chunk allocation when setting block group ro

to the 4.0-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-racy-system-chunk-allocation-when-setting-block-group-ro.patch
and it can be found in the queue-4.0 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, 18 May 2015 19:11:40 +0100
Subject: Btrfs: fix racy system chunk allocation when setting block group ro

From: Filipe Manana <[email protected]>

commit a96295965b600f2dc6ad661c4803c86e87db3d7b upstream.

If while setting a block group read-only we end up allocating a system chunk, through check_system_chunk(), we were not doing it while holding the chunk mutex which is a problem if a concurrent chunk allocation is happening, through do_chunk_alloc(), as it means both block groups can end up using the same logical addresses and physical regions in the device(s). So make sure we hold the chunk mutex.

setting block group ro")

---
 fs/btrfs/extent-tree.c |    2 ++
 fs/btrfs/volumes.c     |    1 +
 2 files changed, 3 insertions(+)

@@ -8548,7 +8548,9 @@ int btrfs_set_block_group_ro(struct btrf
 out:
 	if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
 		alloc_flags = update_block_group_flags(root, cache->flags);
+		lock_chunks(root->fs_info->chunk_root);
 		check_system_chunk(trans, root, alloc_flags);
+		unlock_chunks(root->fs_info->chunk_root);
 	}
 
 	btrfs_end_transaction(trans, root);

@@ -4626,6 +4626,7 @@ int btrfs_alloc_chunk(struct btrfs_trans
 {
 	u64 chunk_offset;
 
+	ASSERT(mutex_is_locked(&extent_root->fs_info->chunk_mutex));
 	chunk_offset = find_next_chunk(extent_root->fs_info);
 	return __btrfs_alloc_chunk(trans, extent_root, chunk_offset, type);
 }

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

queue-4.0/btrfs-fix-racy-system-chunk-allocation-when-setting-block-group-ro.patch