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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id d2-20020a254f02000000b00bdd085da648sm5301898ybb.48.2023.07.05.07.53.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Jul 2023 07:53:13 -0700 (PDT) Sender: Guenter Roeck Message-ID: <7266dc04-8db3-a48b-6844-8530ae7b8adf@roeck-us.net> Date: Wed, 5 Jul 2023 07:53:11 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v3] watchdog: s3c2410: Fix potential deadlock on &wdt->lock Content-Language: en-US To: Chengfeng Ye , 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 In-Reply-To: <20230705090951.63762-1-dg573847474@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) > > -> s3c2410wdt_irq() > -> s3c2410wdt_keepalive() > -> spin_lock(&wdt->lock) (deadlock here) > > [Deadlock Scenario] > s3c2410wdt_probe() > -> s3c2410wdt_start() > -> spin_lock(&wdt->lock) > > -> s3c2410wdt_irq() > -> s3c2410wdt_keepalive() > -> spin_lock(&wdt->lock) (deadlock here) > > [Deadlock Scenario] > s3c2410wdt_keepalive() > -> spin_lock(&wdt->lock) > > -> 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 Reviewed-by: Guenter Roeck > --- > drivers/watchdog/s3c2410_wdt.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c > index 95416a9bdd4b..e1dc71ece01e 100644 > --- a/drivers/watchdog/s3c2410_wdt.c > +++ b/drivers/watchdog/s3c2410_wdt.c > @@ -379,10 +379,11 @@ static int s3c2410wdt_enable(struct s3c2410_wdt *wdt, bool en) > static int s3c2410wdt_keepalive(struct watchdog_device *wdd) > { > struct s3c2410_wdt *wdt = watchdog_get_drvdata(wdd); > + unsigned long flags; > > - spin_lock(&wdt->lock); > + spin_lock_irqsave(&wdt->lock, flags); > writel(wdt->count, wdt->reg_base + S3C2410_WTCNT); > - spin_unlock(&wdt->lock); > + spin_unlock_irqrestore(&wdt->lock, flags); > > return 0; > } > @@ -399,10 +400,11 @@ static void __s3c2410wdt_stop(struct s3c2410_wdt *wdt) > static int s3c2410wdt_stop(struct watchdog_device *wdd) > { > struct s3c2410_wdt *wdt = watchdog_get_drvdata(wdd); > + unsigned long flags; > > - spin_lock(&wdt->lock); > + spin_lock_irqsave(&wdt->lock, flags); > __s3c2410wdt_stop(wdt); > - spin_unlock(&wdt->lock); > + spin_unlock_irqrestore(&wdt->lock, flags); > > return 0; > } > @@ -411,8 +413,9 @@ static int s3c2410wdt_start(struct watchdog_device *wdd) > { > unsigned long wtcon; > struct s3c2410_wdt *wdt = watchdog_get_drvdata(wdd); > + unsigned long flags; > > - spin_lock(&wdt->lock); > + spin_lock_irqsave(&wdt->lock, flags); > > __s3c2410wdt_stop(wdt); > > @@ -433,7 +436,7 @@ static int s3c2410wdt_start(struct watchdog_device *wdd) > writel(wdt->count, wdt->reg_base + S3C2410_WTDAT); > writel(wdt->count, wdt->reg_base + S3C2410_WTCNT); > writel(wtcon, wdt->reg_base + S3C2410_WTCON); > - spin_unlock(&wdt->lock); > + spin_unlock_irqrestore(&wdt->lock, flags); > > return 0; > }