btrfs: Don't call btrfs_start_transaction() on frozen fs to avoid deadlock.

[cascardo/linux.git] / fs / btrfs / super.c

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index c86fb54..6f49b28 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1000,6 +1000,16 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
                         */
                        if (fs_info->pending_changes == 0)
                                return 0;
+                       /*
+                        * A non-blocking test if the fs is frozen. We must not
+                        * start a new transaction here otherwise a deadlock
+                        * happens. The pending operations are delayed to the
+                        * next commit after thawing.
+                        */
+                       if (__sb_start_write(sb, SB_FREEZE_WRITE, false))
+                               __sb_end_write(sb, SB_FREEZE_WRITE);
+                       else
+                               return 0;
                        trans = btrfs_start_transaction(root, 0);
                }
                if (IS_ERR(trans))