btrfs_udpate_root can fail and it aborts the transaction, the correct way to
handle an aborted transaction is to explicitly end with btrfs_end_transaction.
Even now the code is correct since btrfs_commit_transaction would handle an
aborted transaction but this is more of an implementation detail. So let's be
explicit in handling failure in btrfs_update_root.

Furthermore btrfs_commit_transaction can also fail and by ignoring it's return
value we could have left the in-memory copy of the root item in an inconsistent
state. So capture the error value which allows us to correctly revert the RO/RW
flags in case of commit failure.

Signed-off-by: Nikolay Borisov <nbori...@suse.com>
---
 fs/btrfs/ioctl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d6715c2bcdc4..ee4ee7cbba72 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1842,8 +1842,13 @@ static noinline int btrfs_ioctl_subvol_setflags(struct 
file *file,
 
        ret = btrfs_update_root(trans, fs_info->tree_root,
                                &root->root_key, &root->root_item);
+       if (ret < 0) {
+               btrfs_end_transaction(trans);
+               goto out_reset;
+       }
+
+       ret = btrfs_commit_transaction(trans);
 
-       btrfs_commit_transaction(trans);
 out_reset:
        if (ret)
                btrfs_set_root_flags(&root->root_item, root_flags);
-- 
2.7.4

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