btrfs: fix assertion failure during scrub due to block group reallocation

[sfrench/cifs-2.6.git] / fs / btrfs / dev-replace.c

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 71fd99b482832c4e635b761400bc8cc537fc3905..f262026219894c13aed8a0fdd9a38f72aa1a93fb 100644 (file)
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -734,7 +734,12 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 
        btrfs_wait_ordered_roots(fs_info, U64_MAX, 0, (u64)-1);
 
-       /* Commit dev_replace state and reserve 1 item for it. */
+       /*
+        * Commit dev_replace state and reserve 1 item for it.
+        * This is crucial to ensure we won't miss copying extents for new block
+        * groups that are allocated after we started the device replace, and
+        * must be done after setting up the device replace state.
+        */
        trans = btrfs_start_transaction(root, 1);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);