[PATCH 4.0 024/148] Btrfs: fix racy system chunk allocation when setting block group ro

[Greg Kroah-Hartman]

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Filipe Manana <fdmanana@xxxxxxxx>

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.

Fixes: 2f0810880f08 ("btrfs: delete chunk allocation attemp when
                      setting block group ro")

Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -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);
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -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);
 }


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