Re: [Devel] [PATCH hci-8.1 3/7] drivers/md/dm-qcow2: prepare process_one_qio() for fastpath

[Konstantin Khorenko <khorenko@virtuozzo.com>]

I won't apply this version, please send v2 with the changes below.

On Thu, 29 Oct 2026 17:03:42 +0300, Andrey Zhadchenko wrote:
>  static int handle_metadata(struct qcow2 *qcow2, struct qio **qio,
> -			   struct qcow2_map *map)
> +			   struct qcow2_map *map, bool avoid_metadata_changes)
>  {
>  	bool write = op_is_write((*qio)->bi_op);
>  	int ret;

Item 2 of the cover letter reply: pass the flag into parse_metadata()
and return to the slow path before qcow2_handle_r1r2_maps().

Why: for COW writes and cluster unmapping discards parse_metadata()
looks up the R1 and R2 pages before this function decides to go slow,
so the fast path reads them for nothing. The comment above
__handle_r1r2_maps() says R1 is unstable outside the main kwork. If the
R1 page is not cached, submit_read_md_page() drops the lock and inserts
it under the old page id; when relocate_refcount_table() has renumbered
the cached R1 pages meanwhile, a stale copy of the old R1 cluster stays
in the cache under an id whose cluster relocate then frees.

Alexander's remarks on the typo and on the literal 2 still need an
answer (item 7).

-- 
Konstantin Khorenko,
Virtuozzo Linux Kernel Team

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