Re: [PATCH] btrfs: drop recovered reloc root refs on recovery failure

[David Sterba <dsterba@suse.cz>]

On Sun, Jul 12, 2026 at 04:22:32AM +0000, Guanghui Yang wrote:
> During relocation recovery, each fs root gets a reference to its relocation
> root. If loading or adding a later root fails, or if the first transaction
> commit fails, btrfs_recover_relocation() jumps to out_unset before
> merge_reloc_roots() and clean_dirty_subvols().
> 
> put_reloc_control() drops the list-owned relocation root references, but it
> does not clear fs_root->reloc_root or drop the references owned by those
> pointers. Mount cleanup only drops them when BTRFS_FS_ERROR is set, so an
> error such as -ENOMEM while processing a later root can leave references
> behind.
> 
> Keep temporary references to the fs roots associated during recovery. On
> failure, clear their reloc_root pointers and drop the corresponding
> references. Once the first transaction commit succeeds, drop only the
> temporary fs root references and let the normal merge and cleanup paths
> handle the relocation roots.
> 
> Fault injection on a pending-relocation image confirmed the cleanup gap.
> With an injected first-commit failure, 25 fs roots had reloc_root set with
> fs_error=0. With this fix, the same failure path drops that count to 0
> before mount fails.
> 
> Fixes: f44deb7442ed ("btrfs: hold a ref on the root->reloc_root")
> Cc: stable@vger.kernel.org
> Signed-off-by: Guanghui Yang <3497809730@qq.com>

Added to for-next, thanks.