linux-kernel - Re: [PATCH 16/18] lib/stackdepot: annotate racy slab

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Message-ID: <CA+fCnZdwuAm-fD-o2Yq86=NgU=YympuwAmERN9KwjpYfkPeYLg@mail.gmail.com>
Date:   Tue, 31 Jan 2023 19:57:58 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     andrey.konovalov@...ux.dev,
        Alexander Potapenko <glider@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 16/18] lib/stackdepot: annotate racy slab_index accesses

On Tue, Jan 31, 2023 at 9:41 AM Marco Elver <elver@...gle.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!