From aeb3ef51b602dce456c850414aa1becd0e7aeab1 Mon Sep 17 00:00:00 2001 From: Chengfeng Ye Date: Wed, 5 Jul 2023 09:09:51 +0000 Subject: [PATCH] watchdog: s3c2410: Fix potential deadlock on &wdt->lock 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: Krzysztof Kozlowski Reviewed-by: Guenter Roeck Link: https://lore.kernel.org/r/20230705090951.63762-1-dg573847474@gmail.com Signed-off-by: Guenter Roeck Signed-off-by: Wim Van Sebroeck --- 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 2bcc8faa7fa5..0b4bd883ff28 100644 --- a/drivers/watchdog/s3c2410_wdt.c +++ b/drivers/watchdog/s3c2410_wdt.c @@ -378,10 +378,11 @@ 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; } @@ -398,10 +399,11 @@ 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; } @@ -410,8 +412,9 @@ 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); @@ -432,7 +435,7 @@ 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; }