Re: [PATCH] dm thin metadata: fix superblock refcount leak on snapshot shadow failure

Ming Hung Tsai <[email protected]> Mon, 13 Jul 2026 10:40:48 +0800

Newsgroups	dev.linux.lists.dm-devel,org.kernel.vger.linux-kernel
Message-ID	<CALjSBEtD00yuLaBJXtJjFG7L0nCLRaGDUVGoN7VZ4wkVRD0CDQ@mail.gmail.com>

On Sat, Jul 11, 2026 at 6:16 PM Genjian <[email protected]> wrote:
>
> From: Genjian Zhang <[email protected]>
>
> __reserve_metadata_snap() increments THIN_SUPERBLOCK_LOCATION in the
> metadata space map before shadowing it. When dm_tm_shadow_block()
> fails, a reference is leaked in the metadata space map.
>
> Fix by adding the missing dm_sm_dec_block().
>
> Fixes: cc8394d86f04 ("dm thin: provide userspace access to pool metadata")
> Signed-off-by: Genjian Zhang <[email protected]>
> ---

The fix looks reasonable as a best-effort cleanup for the immediate
refcount leak.