linux-kernel - Re: [PATCH v2] watchdog: s3c2410: Fix potential deadlock on &wdt->lock

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Message-ID: <CAAo+4rW+bU-M=Wb16yMev8i3tdafH1p1bryCkKygDsShQ08n0w@mail.gmail.com>
Date:   Wed, 5 Jul 2023 17:01:54 +0800
From:   Chengfeng Ye <dg573847474@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     alim.akhtar@...sung.com, wim@...ux-watchdog.org,
        linux@...ck-us.net, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] watchdog: s3c2410: Fix potential deadlock on &wdt->lock

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@...aro.org> 于2023年7月5日周三 16:58写道：
>
> 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@...il.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
>