Relocation of a data block group creates ordered extents. They can cause a
hang when a process is trying to thaw the filesystem.
We should have called sb_start_write(), so the filesystem is not being
frozen. Add an ASSERT to check it is protected.
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
fs/btrfs/relocation.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index fdc2c4b411f0..5e52cd8d5f23 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3977,6 +3977,16 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
if (!bg)
return -ENOENT;
+ /*
+ * Relocation of a data block group creates ordered extents.
+ * Without sb_start_write(), we can freeze the FS while unfinished
+ * ordered extents are left. Such ordered extents can cause a
+ * deadlock e.g, when syncfs() is trying to finish them because
+ * they never finish as the FS is already frozen.
+ */
+ if (bg->flags & BTRFS_BLOCK_GROUP_DATA)
+ ASSERT(sb_write_started(fs_info->sb));
+
if (btrfs_pinned_by_swapfile(fs_info, bg)) {
btrfs_put_block_group(bg);
return -ETXTBSY;
--
2.35.1
