btrfs: do not BUG_ON() on failure to migrate space when replacing extents

At btrfs_replace_file_extents(), if we fail to migrate reserved metadata
space from the transaction block reserve into the local block reserve,
we trigger a BUG_ON(). This is because it should not be possible to have
a failure here, as we reserved more space when we started the transaction
than the space we want to migrate. However having a BUG_ON() is way too
drastic, we can perfectly handle the failure and return the error to the
caller. So just do that instead, and add a WARN_ON() to make it easier
to notice the failure if it ever happens (which is particularly useful
for fstests, and the warning will trigger a failure of a test case).

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8e7fb3e..dd30639 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2718,7 +2718,8 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 
        ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
                                      min_size, false);
-       BUG_ON(ret);
+       if (WARN_ON(ret))
+               goto out_trans;
        trans->block_rsv = rsv;
 
        cur_offset = start;
@@ -2837,7 +2838,8 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 
                ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
                                              rsv, min_size, false);
-               BUG_ON(ret);    /* shouldn't happen */
+               if (WARN_ON(ret))
+                       break;
                trans->block_rsv = rsv;
 
                cur_offset = drop_args.drop_end;