Btrfs: fix wrong generation check of super block on a seed device

The super block generation of the seed devices is not the same as the
filesystem which sprouted from them because we don't update the super
block on the seed devices when we change that new filesystem. So we
should not use the generation of that new filesystem to check the super
block generation on the seed devices, Fix it.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
(cherry picked from commit 5f546063cee93047af90cf2756e023da9f9fca51)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 57b7d12beb0218030692d8c02bc57fa1a1a569d5..b99ab5e5c2b27ca9115e9a66eff193a608826bb7 100644 (file)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2832,7 +2832,11 @@ static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
        if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
                return -EIO;
 
-       gen = root->fs_info->last_trans_committed;
+       /* Seed devices of a new filesystem has their own generation. */
+       if (scrub_dev->fs_devices != root->fs_info->fs_devices)
+               gen = scrub_dev->generation;
+       else
+               gen = root->fs_info->last_trans_committed;
 
        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                bytenr = btrfs_sb_offset(i);