Re: [PATCH 16/18] lib/stackdepot: annotate racy slab_index accesses

From: Andrey Konovalov <andreyknvl@gmail.com>
To: Marco Elver <elver@google.com>
Cc: andrey.konovalov@linux.dev,
	Alexander Potapenko <glider@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	kasan-dev@googlegroups.com, Evgenii Stepanov <eugenis@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH 16/18] lib/stackdepot: annotate racy slab_index accesses
Date: Tue, 31 Jan 2023 19:57:58 +0100	[thread overview]
Message-ID: <CA+fCnZdwuAm-fD-o2Yq86=NgU=YympuwAmERN9KwjpYfkPeYLg@mail.gmail.com> (raw)
In-Reply-To: <CANpmjNNzNSDrxfrZUcRtt7=hV=Mz8_kyCpqVnyAqzhaiyipXCg@mail.gmail.com>

On Tue, Jan 31, 2023 at 9:41 AM Marco Elver <elver@google.com> wrote:
>
> > diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> > index f291ad6a4e72..cc2fe8563af4 100644
> > --- a/lib/stackdepot.c
> > +++ b/lib/stackdepot.c
> > @@ -269,8 +269,11 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
> >                         return NULL;
> >                 }
> >
> > -               /* Move on to the next slab. */
> > -               slab_index++;
> > +               /*
> > +                * Move on to the next slab.
> > +                * WRITE_ONCE annotates a race with stack_depot_fetch.
>
> "Pairs with potential concurrent read in stack_depot_fetch()." would be clearer.
>
> I wouldn't say WRITE_ONCE annotates a race (race = involves 2+
> accesses, but here's just 1), it just marks this access here which
> itself is paired with the potential racing read in the other function.

Will do in v2. Thanks!