linux-kernel - Re: [PATCH v2 2/2] watchdog: dw_wdt: keepalive the watchdog at write time

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Message-ID: <20150508052404.GB18159@dtor-ws>
Date:	Thu, 7 May 2015 22:24:04 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	wim@...ana.be, linux@...ck-us.net, jszhang@...vell.com,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] watchdog: dw_wdt: keepalive the watchdog at write
 time

On Thu, May 07, 2015 at 09:27:45PM -0700, Doug Anderson wrote:
> If you've got code that does this in a tight loop
>   1. Open watchdog
>   2. Send 'expect close'
>   3. Close watchdog
> ...you'll eventually trigger a watchdog reset.  You can reproduce this
> by using daisydog (1) and running:
>   while true; do daisydog -c > /dev/null; done
> 
> The problem is that each time you write to the watchdog for 'expect
> close' it moves the timer .5 seconds out.  The timer thus never fires
> and never pats the watchdog for you.
> 
> 1: http://git.chromium.org/gitweb/?p=chromiumos/third_party/daisydog.git
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> Tested-by: Jisheng Zhang <jszhang@...vell.com>

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

> ---
> Changes in v2: None
> 
>  drivers/watchdog/dw_wdt.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> index a284abd..6ea0634 100644
> --- a/drivers/watchdog/dw_wdt.c
> +++ b/drivers/watchdog/dw_wdt.c
> @@ -215,6 +215,7 @@ static ssize_t dw_wdt_write(struct file *filp, const char __user *buf,
>  	}
>  
>  	dw_wdt_set_next_heartbeat();
> +	dw_wdt_keepalive();
>  	mod_timer(&dw_wdt.timer, jiffies + WDT_TIMEOUT);
>  
>  	return len;
> -- 
> 2.2.0.rc0.207.ga3a616c
> 

-- 
Dmitry
--
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