1 files changed, 10 insertions, 0 deletions
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 169baa817d96..d8e539fe5544 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1304,6 +1304,16 @@ struct btrfs_fs_info {
 	 * so it is also safe.
 	 */
 	u64 max_inline;
+	/*
+	 * Protected by ->chunk_mutex and sb->s_umount.
+	 *
+	 * The reason that we use two lock to protect it is because only
+	 * remount and mount operations can change it and these two operations
+	 * are under sb->s_umount, but the read side (chunk allocation) can not
+	 * acquire sb->s_umount or the deadlock would happen. So we use two
+	 * locks to protect it. On the write side, we must acquire two locks,
+	 * and on the read side, we just need acquire one of them.
+	 */
 	u64 alloc_start;
 	struct btrfs_transaction *running_transaction;
 	wait_queue_head_t transaction_throttle;