Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230705072304.37741-1-dg573847474@gmail.com> <d15656f4-0d39-fbaf-884a-77935cd69e3f@linaro.org>
In-Reply-To: <d15656f4-0d39-fbaf-884a-77935cd69e3f@linaro.org>
From:   Chengfeng Ye <dg573847474@gmail.com>
Date:   Wed, 5 Jul 2023 17:01:54 +0800
Message-ID: <CAAo+4rW+bU-M=Wb16yMev8i3tdafH1p1bryCkKygDsShQ08n0w@mail.gmail.com>
Subject: Re: [PATCH v2] watchdog: s3c2410: Fix potential deadlock on &wdt->lock
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     alim.akhtar@samsung.com, wim@linux-watchdog.org,
        linux@roeck-us.net, linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-watchdog@vger.kernel.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Hi Krzysztof,

Thanks for the reminder!

I didn't notice that s3c2410wdt_keepalive() can also be called from
.ping callback. Would send a v3 patch soon.

Best Regards,
Chengfeng

Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> =E4=BA=8E2023=E5=B9=B4=
7=E6=9C=885=E6=97=A5=E5=91=A8=E4=B8=89 16:58=E5=86=99=E9=81=93=EF=BC=9A
>
> On 05/07/2023 09:23, Chengfeng Ye wrote:
> > As &wdt->lock is acquired by hard irq s3c2410wdt_irq(), other
> > acquisition of the same lock under process context should
> > disable irq, otherwise deadlock could happen if the irq preempt
> > the execution while the lock is held in process context on the
> > same CPU.
> >
> > [Deadlock Scenario]
> > s3c2410wdt_suspend()
> >     -> s3c2410wdt_stop()
> >     -> spin_lock(&wdt->lock)
> >         <irq iterrupt>
> >         -> s3c2410wdt_irq()
> >         -> s3c2410wdt_keepalive()
> >         -> spin_lock(&wdt->lock) (deadlock here)
> >
> > [Deadlock Scenario]
> > s3c2410wdt_probe()
> >     -> s3c2410wdt_start()
> >     -> spin_lock(&wdt->lock)
> >         <irq iterrupt>
> >         -> s3c2410wdt_irq()
> >         -> s3c2410wdt_keepalive()
> >         -> spin_lock(&wdt->lock) (deadlock here)
> >
> > This flaw was found by an experimental static analysis tool I am
> > developing for irq-related deadlock, which reported the above
> > warning when analyzing the linux kernel 6.4-rc7 release.
> >
> > The tentative patch fix the potential deadlock by spin_lock_irqsave()
> > under process context.
> >
> > Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
> > ---
> >  drivers/watchdog/s3c2410_wdt.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_=
wdt.c
> > index 95416a9bdd4b..2dfc0d6a3004 100644
> > --- a/drivers/watchdog/s3c2410_wdt.c
> > +++ b/drivers/watchdog/s3c2410_wdt.c
> > @@ -399,10 +399,11 @@ static void __s3c2410wdt_stop(struct s3c2410_wdt =
*wdt)
>
> Why you didn't update also s3c2410wdt_keepalive()?
>
> Best regards,
> Krzysztof
>