linux-kernel - Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4 13/17] khwasan: add hooks implementation)

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Message-ID: <CANn89iLjk-mV3kZGASvZQtYaBDy9sbo=NW4Tt_V=dOP_-b=VNQ@mail.gmail.com>
Date:   Tue, 31 Jul 2018 11:16:28 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        "Theodore Ts'o" <tytso@....edu>, jack@...e.com,
        linux-ext4@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Florian Westphal <fw@...len.de>,
        David Miller <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev <netdev@...r.kernel.org>,
        Gerrit Renker <gerrit@....abdn.ac.uk>, dccp@...r.kernel.org,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, airlied@...ux.ie,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Ursula Braun <ubraun@...ux.ibm.com>,
        linux-s390@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4
 13/17] khwasan: add hooks implementation)

On Tue, Jul 31, 2018 at 10:51 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
>
> Is it OK to overwrite ct->status? It seems that are some read and
> writes to it right after atomic_inc_not_zero.

If it is after a (successful) atomic_inc_not_zero(),
the object is guaranteed to be alive (not freed or about to be freed).

About readind/writing a specific field, all traditional locking rules apply.

For TCP socket, we would generally grab the socket lock before
reading/writing various fields.

ct->status seems to be manipulated with set_bit() and clear_bit()
which are SMP safe.