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Sender: Guenter Roeck <groeck7@gmail.com>
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Date:   Wed, 5 Jul 2023 05:51:41 -0700
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Subject: Re: [PATCH v3] watchdog: s3c2410: Fix potential deadlock on
 &wdt->lock
Content-Language: en-US
To:     Chengfeng Ye <dg573847474@gmail.com>,
        krzysztof.kozlowski@linaro.org, alim.akhtar@samsung.com,
        wim@linux-watchdog.org
Cc:     linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-watchdog@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230705090951.63762-1-dg573847474@gmail.com>
From:   Guenter Roeck <linux@roeck-us.net>
In-Reply-To: <20230705090951.63762-1-dg573847474@gmail.com>
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On 7/5/23 02:09, 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)
> 
> [Deadlock Scenario]
> s3c2410wdt_keepalive()
>      -> 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>

I am sure you know what you changed in each version of your patches. I don't.
Please provide change logs when you send new versions of your patches.

Guenter