linux-kernel - Re: [PATCH] mm: swap: prevent possible data-race in __try_to_reclaim

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Message-ID: <CAO9qdTHUW+SRkLsxdO_PXKw7qGvXKCWfa1GtVYNrnyGWEUe0Mw@mail.gmail.com>
Date: Tue, 8 Oct 2024 11:35:03 +0900
From: Jeongjun Park <aha310510@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev, 
	kasong@...cent.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	syzbot+fa43f1b63e3aa6f66329@...kaller.appspotmail.com
Subject: Re: [PATCH] mm: swap: prevent possible data-race in __try_to_reclaim_swap

Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Mon, 7 Oct 2024 13:06:49 +0800 kernel test robot <lkp@...el.com> 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@intel.com/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@intel.com/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@...el.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202410071223.t0yF8vP8-lkp@intel.com/
> >
> > 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