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From: Dmitry Vyukov <dvyukov@google.com>
Date: Wed, 1 Aug 2018 15:52:40 +0200
Message-ID: <CACT4Y+ay6+UTLMr4K_RTTubjzpGZXe2n7T8Q=kC=Q1baHshkHQ@mail.gmail.com>
Subject: Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4
 13/17] khwasan: add hooks implementation)
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To: Florian Westphal <fw@strlen.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Christoph Lameter <cl@linux.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>, linux-ext4@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Pablo Neira Ayuso <pablo@netfilter.org>, Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>, David Miller <davem@davemloft.net>, NetFilter <netfilter-devel@vger.kernel.org>, coreteam@netfilter.org, Network Development <netdev@vger.kernel.org>, Gerrit Renker <gerrit@erg.abdn.ac.uk>, dccp@vger.kernel.org, Jani Nikula <jani.nikula@linux.intel.com>, Joonas Lahtinen <joonas.lahtinen@linux.intel.com>, Rodrigo Vivi <rodrigo.vivi@intel.com>, Dave Airlie <airlied@linux.ie>, intel-gfx <intel-gfx@lists.freedesktop.org>, DRI <dri-devel@lists.freedesktop.org>, Eric Dumazet <edumazet@google.com>, Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>, Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>, Ursula Braun <ubraun@linux.ibm.com>, linux-s390 <linux-s390@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, Andrey Konovalov <andreyknvl@google.com>

On Wed, Aug 1, 2018 at 3:46 PM, Florian Westphal <fw@strlen.de> wrote:
> Dmitry Vyukov <dvyukov@google.com> wrote:
>> If that scenario is possible that a fix would be to make
>
> Looks possible.
>
>> __nf_conntrack_find_get ever return NULL iff it got NULL from
>> ____nf_conntrack_find (not if any of the checks has failed).
>
> I don't see why we need to restart on nf_ct_is_dying(), but other
> than that this seems ok.

Because it can be a wrong entry dying. When we check dying, we don't
yet know if we are looking at the right entry or not. If we
successfully acquire a reference, then recheck nf_ct_key_equal and
_then_ check dying, then we don't need to restart on dying. But with
the current check order, we need to restart on dying too.