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

[Andrew Morton]

On Wed, 16 Sep 2026 10:34:46 +0200 Arnd Bergmann <arnd@xxxxxxxxxx> wrote:

> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> I previously worked around a false-postive gcc-16 warning in the
> get_tier_idx() function, by adding a fake initializer. This happens with
> the -fsanitize=bounds sanitizer when the compiler creates a specialized
> variant of isolate_folios():
> 
> In function 'get_tier_idx',
>     inlined from 'isolate_folios.constprop' at mm/vmscan.c:4982:9:
> mm/vmscan.c:4934:9: error: 'sp.refaulted' is used uninitialized [-Werror=uninitialized]
>  4934 |         read_ctrl_pos(lruvec, type, LRU_TIER_MIN, LRU_TIER_MIN, 2, &sp);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/vmscan.c: In function 'isolate_folios.constprop':
> mm/vmscan.c:4946:25: note: 'sp.refaulted' was declared here
>  4946 |         struct ctrl_pos sp, pv = {};
>       |                         ^~
> 
> Adding another "= {}" would solve the problem as well, but to prevent
> this from happening again after the next code refactoring, try instead to
> prevent this by forbidding interprocedural optimizations on this function.
>
> Link: https://lore.kernel.org/all/20260213123902.3466040-1-arnd@xxxxxxxxxx/
> Fixes: 3de705a43a46 ("mm/vmscan: avoid false-positive -Wuninitialized warning")

I believe we want older kernel to compile properly with gcc-16, so I'm
suggesting this be backported?

Perhaps we should have done that with 3de705a43a46 also.