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

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Date:   Wed, 5 Jul 2023 10:57:58 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Chengfeng Ye <dg573847474@...il.com>, alim.akhtar@...sung.com,
        wim@...ux-watchdog.org, linux@...ck-us.net
Cc:     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

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