Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
MIME-Version: 1.0
References: <20231115210509.481514-1-vschneid@redhat.com> <20231115210509.481514-2-vschneid@redhat.com>
 <CANn89iJPxrXi35=_OJqLsJjeNU9b8EFb_rk+EEMVCMiAOd2=5A@mail.gmail.com>
 <CAD235PRWd+zF1xpuXWabdgMU01XNpvtvGorBJbLn9ny2G_TSuw@mail.gmail.com> <CANn89iKRSKz0e8v+Z-UsKGs4fQWDt6eTAw71VENbSmfkEicTPA@mail.gmail.com>
In-Reply-To: <CANn89iKRSKz0e8v+Z-UsKGs4fQWDt6eTAw71VENbSmfkEicTPA@mail.gmail.com>
From:   Valentin Schneider <vschneid@redhat.com>
Date:   Thu, 23 Nov 2023 17:45:29 +0100
Message-ID: <CAD235PTyEce0S-22vg=opQdq0MUwEovdx5henU=9Mwh3Rf8QrA@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] tcp/dcpp: Un-pin tw_timer
To:     Eric Dumazet <edumazet@google.com>
Cc:     dccp@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        David Ahern <dsahern@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Tomas Glozar <tglozar@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, 23 Nov 2023 at 17:32, Eric Dumazet <edumazet@google.com> wrote:
>
> On Thu, Nov 23, 2023 at 3:34=E2=80=AFPM Valentin Schneider <vschneid@redh=
at.com> wrote:
> > I thought that was already the case, per inet_twsk_hashdance():
> >
> > /* tw_refcnt is set to 3 because we have :
> >  * - one reference for bhash chain.
> >  * - one reference for ehash chain.
> >  * - one reference for timer.
> >
> > and
> >
> > tw_timer_handler()
> > `\
> >   inet_twsk_kill()
> >   `\
> >     inet_twsk_put()
> >
> > So AFAICT, after we go through the hashdance, there's a reference on
> > tw_refcnt held by the tw_timer.
> > inet_twsk_deschedule_put() can race with arming the timer, but it only
> > calls inet_twsk_kill() if the timer
> > was already armed & has been deleted, so there's no risk of calling it
> > twice... If I got it right :-)
> >
>
> Again, I think you missed some details.
>
> I am OOO for a few days, I do not have time to elaborate.
>
> You will need to properly track active timer by elevating
> tw->tw_refcnt, or I guarantee something wrong will happen.
>

Gotcha, let me dig into this then!