Re: [PATCH] mm: swap: prevent possible data-race in __try_to_reclaim_swap

[Jeongjun Park]

Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, 7 Oct 2024 13:06:49 +0800 kernel test robot <lkp@xxxxxxxxx> wrote:
>
> > Hi Jeongjun,
> >
> > kernel test robot noticed the following build warnings:
> >
> > [auto build test WARNING on akpm-mm/mm-everything]
> >
> > url:    https://github.com/intel-lab-lkp/linux/commits/Jeongjun-Park/mm-swap-prevent-possible-data-race-in-__try_to_reclaim_swap/20241004-222733
> > base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> > patch link:    https://lore.kernel.org/r/20241004142504.4379-1-aha310510%40gmail.com
> > patch subject: [PATCH] mm: swap: prevent possible data-race in __try_to_reclaim_swap
> > config: x86_64-kexec (https://download.01.org/0day-ci/archive/20241007/202410071223.t0yF8vP8-lkp@xxxxxxxxx/config)
> > compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241007/202410071223.t0yF8vP8-lkp@xxxxxxxxx/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202410071223.t0yF8vP8-lkp@xxxxxxxxx/
> >
> > All warnings (new ones prefixed by >>):
> >
> > >> mm/swapfile.c:203:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
> >      203 |         if (!folio_trylock(folio))
> >          |             ^~~~~~~~~~~~~~~~~~~~~
> >    mm/swapfile.c:254:9: note: uninitialized use occurs here
> >      254 |         return ret;
>
> This warning can't be correct?

I think it's correct. Even if folio_trylock fails, the return value
should be -nr_pages. Not initializing ret like in the v1 patch
goes against the design purpose of the function.

So I think it's right to apply the v2 patch that I sent you.

Regards,
Jeongjun Park