Re: [PATCH] kasan,kmsan: remove __GFP_KSWAPD_RECLAIM usage from kasan/kmsan

From: Alexander Potapenko <glider@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Huang, Ying" <ying.huang@intel.com>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	 syzbot <syzbot+ece2915262061d6e0ac1@syzkaller.appspotmail.com>,
	 syzkaller-bugs@googlegroups.com,
	Mel Gorman <mgorman@techsingularity.net>,
	 Vlastimil Babka <vbabka@suse.cz>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	 Dmitry Vyukov <dvyukov@google.com>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	 Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Marco Elver <elver@google.com>,
	 kasan-dev <kasan-dev@googlegroups.com>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH] kasan,kmsan: remove __GFP_KSWAPD_RECLAIM usage from kasan/kmsan
Date: Wed, 21 Jun 2023 17:37:09 +0200	[thread overview]
Message-ID: <CAG_fn=W5-+3Xz2LcJW=kbbV+91U8W5MLfAFtR+eNLYXG0v=zKQ@mail.gmail.com> (raw)
In-Reply-To: <20230609153124.11905393c03660369f4f5997@linux-foundation.org>

On Sat, Jun 10, 2023 at 12:31 AM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Wed, 31 May 2023 15:31:53 +0200 Alexander Potapenko <glider@google.com> wrote:
>
> > On Mon, May 29, 2023 at 3:08 AM Huang, Ying <ying.huang@intel.com> wrote:
> > >
> > > ? Handa <penguin-kernel@I-love.SAKURA.ne.jp> writes:
> > >
> > > > syzbot is reporting lockdep warning in __stack_depot_save(), for
> > > > the caller of __stack_depot_save() (i.e. __kasan_record_aux_stack() in
> > > > this report) is responsible for masking __GFP_KSWAPD_RECLAIM flag in
> > > > order not to wake kswapd which in turn wakes kcompactd.
> > > >
> > > > Since kasan/kmsan functions might be called with arbitrary locks held,
> > > > mask __GFP_KSWAPD_RECLAIM flag from all GFP_NOWAIT/GFP_ATOMIC allocations
> > > > in kasan/kmsan.
> > > >
> > > > Note that kmsan_save_stack_with_flags() is changed to mask both
> > > > __GFP_DIRECT_RECLAIM flag and __GFP_KSWAPD_RECLAIM flag, for
> > > > wakeup_kswapd() from wake_all_kswapds() from __alloc_pages_slowpath()
> > > > calls wakeup_kcompactd() if __GFP_KSWAPD_RECLAIM flag is set and
> > > > __GFP_DIRECT_RECLAIM flag is not set.
> > > >
> > > > Reported-by: syzbot <syzbot+ece2915262061d6e0ac1@syzkaller.appspotmail.com>
> > > > Closes: https://syzkaller.appspot.com/bug?extid=ece2915262061d6e0ac1
> > > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > >
> > > This looks good to me.  Thanks!
> > >
> > > Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> >
> > Sorry for the late reply, but maybe it would be better to mask this
> > flag in __stack_depot_save() (lib/stackdepot.c) instead?
> > We are already masking out a number of flags there, and the problem
> > seems quite generic.
>
>
> Tetsuo?

Reviewed-by: Alexander Potapenko <glider@google.com>

Andrew, please accept this patch. As noted in the other thread, no
changes to stackdepot are needed.

-- 
Alexander Potapenko
Software Engineer

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