[PATCH AUTOSEL 5.15 25/41] btrfs: do not BUG_ON() on failure to migrate space when replacing extents

[Sasha Levin <sashal@kernel.org>]

From: Filipe Manana <fdmanana@suse.com>

[ Upstream commit 650c9caba32a0167a018cca0fab32a2965d23513 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/file.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 07ec05a810b4..a4849a7001e6 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2745,7 +2745,8 @@ 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;
@@ -2864,7 +2865,8 @@ 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;
-- 
2.35.1