Re: [PATCH v3 01/18] mm/swap: fix off-by-one in swap cache replace sanity check

[Barry Song]

On Fri, Aug 21, 2026 at 2:55 AM Kairui Song via B4 Relay
<devnull+kasong.tencent.com@xxxxxxxxxx> wrote:
>
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> The DEBUG_VM sanity check in __swap_cache_replace_folio() iterates
> the old folio's range with "while (ci_off++ < ci_end)", so the loop
> body runs on the already-incremented offset: the first entry is
> skipped and one entry past the range is read.  For a folio split
> that entry belongs to the first after-split folio and was just
> repointed by the replacement loop above, so the check would warn
> spuriously whenever sub-folio orders differ from the head folio's,
> as non-uniform swapcache splits now do.
>
> Use the same do-while pattern as the replacement loop.
>
> Fixes: 8578e0c00dcf ("mm, swap: use the swap table for the swap cache and switch API")
> Acked-by: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>

LGTM, thanks!

Reviewed-by: Barry Song <baohua@xxxxxxxxxx>