Re: [PATCH] [v2] mm/vmscan: avoid false-positive -Wuninitialized warning

[Barry Song <baohua@kernel.org>]

On Tue, Apr 14, 2026 at 2:52 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When the -fsanitize=bounds sanitizer is enabled, gcc-16 sometimes runs
> into a corner case in the read_ctrl_pos() pos function, where it sees
> possible undefined behavior from the 'tier' index overflowing, presumably
> in the case that this was called with a negative tier:
>
> In function 'get_tier_idx',
>     inlined from 'isolate_folios' at mm/vmscan.c:4671:14:
> mm/vmscan.c: In function 'isolate_folios':
> mm/vmscan.c:4645:29: error: 'pv.refaulted' is used uninitialized [-Werror=uninitialized]
>
> Part of the problem seems to be that read_ctrl_pos() has unusual calling
> conventions since commit 37a260870f2c ("mm/mglru: rework type selection")
> where passing MAX_NR_TIERS makes it accumulate all tiers but passing a
> smaller positive number makes it read a single tier instead.
>
> Shut up the warning by adding a fake initialization to the two instances
> of this variable that can run into that corner case.
>
> Link: https://lore.kernel.org/all/CAJHvVcjtFW86o5FoQC8MMEXCHAC0FviggaQsd5EmiCHP+1fBpg@mail.gmail.com/
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v2: replace the earlier more invasive cleanup with a trivial
>     workaround

Reviewed-by: Barry Song <baohua@kernel.org>