linux-kernel - Re: [RFC 1/3] watchdog: change watchdog_need

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Date:	Sun, 17 Jul 2016 22:30:31 +0200
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/3] watchdog: change watchdog_need_worker logic

Hi Guenter,

> On 07/17/2016 12:24 PM, Wim Van Sebroeck wrote:
> >Hi Rasmus,
> >
> >>If the driver indicates that the watchdog is running, the framework
> >>should feed it until userspace opens the device, regardless of whether
> >>the driver has set max_hw_heartbeat_ms.
> >>
> >>This patch only affects the case where wdd->max_hw_heartbeat_ms is
> >>zero, wdd->timeout is non-zero, the watchdog is not active and the
> >>hardware device is running (*):
> >>
> >>- If wdd->timeout is zero, watchdog_need_worker() returns false both
> >>before and after this patch, and watchdog_next_keepalive() is not
> >>called.
> >>
> >>- If watchdog_active(wdd), the return value from watchdog_need_worker
> >>is also the same as before (namely, hm && t > hm). Hence in that case,
> >>watchdog_next_keepalive() is only called if hm == max_hw_heartbeat_ms
> >>is non-zero, so the change to min_not_zero there is a no-op.
> >>
> >>- If the watchdog is not active and the device is not running, we
> >>return false from watchdog_need_worker just as before.
> >>
> >>That leaves the watchdog_hw_running(wdd) && !watchdog_active(wdd) &&
> >>wdd->timeout case. Again, it's easy to see that if
> >>wdd->max_hw_heartbeat_ms is non-zero, we return true from
> >>watchdog_need_worker with and without this patch, and the logic in
> >>watchdog_next_keepalive is unchanged. Finally, if
> >>wdd->max_hw_heartbeat_ms is 0, we used to end up in the
> >>cancel_delayed_work branch, whereas with this patch we end up
> >>scheduling a ping timeout_ms/2 from now.
> >>
> >>(*) This should imply that no current kernel drivers are affected,
> >>since the only drivers which explicitly set WDOG_HW_RUNNING are
> >>imx2_wdt.c and dw_wdt.c, both of which also provide a non-zero value
> >>for max_hw_heartbeat_ms. The watchdog core also sets WDOG_HW_RUNNING,
> >>but only when the driver doesn't provide ->stop, in which case it
> >>must, according to Documentation/watchdog/watchdog-kernel-api.txt, set
> >>max_hw_heartbeat_ms.
> >
> >This isn't completely true. We will have the following in the 
> >linux-watchdog tree:
> >drivers/watchdog/aspeed_wdt.c:		set_bit(WDOG_HW_RUNNING, 
> >&wdt->wdd.status);
> >drivers/watchdog/dw_wdt.c:	set_bit(WDOG_HW_RUNNING, &wdd->status);
> >drivers/watchdog/dw_wdt.c:		set_bit(WDOG_HW_RUNNING, 
> >&wdd->status);
> >drivers/watchdog/imx2_wdt.c:	set_bit(WDOG_HW_RUNNING, &wdog->status);
> >drivers/watchdog/imx2_wdt.c:		set_bit(WDOG_HW_RUNNING, 
> >&wdog->status);
> >drivers/watchdog/max77620_wdt.c:		set_bit(WDOG_HW_RUNNING, 
> >&wdt_dev->status);
> >drivers/watchdog/sbsa_gwdt.c:		set_bit(WDOG_HW_RUNNING, 
> >&wdd->status);
> >drivers/watchdog/tangox_wdt.c:		set_bit(WDOG_HW_RUNNING, 
> >&dev->wdt.status);
> >
> >I checked the ones that aren't mentioned and aspeed_wdt, max77620_wdt and 
> >sbsa_gwdt.c
> >also have a non-zero value for max_hw_heartbeat_ms. But tangox_wdt.c 
> >doesn't set it.
> >This one will need to be looked at closer.
> >
> 
> I had a brief look; the tangox_wdt problem is my fault. I overlooked that 
> with
> my commit 'watchdog: tangox: Mark running watchdog correctly'.
> 
> We have a number of options: Set max_hw_heartbeat_ms in tangox_wdt.c,
> accept this patch, or both. I think we should accept this patch.

We accept this patch and add a fix for tangox_wdt.c .

> 
> Thanks,
> Guenter
> 
> >>
> >>Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> >>---
> >>  drivers/watchdog/watchdog_dev.c | 10 +++++++---
> >>  1 file changed, 7 insertions(+), 3 deletions(-)
> >>
> >>diff --git a/drivers/watchdog/watchdog_dev.c 
> >>b/drivers/watchdog/watchdog_dev.c
> >>index 3595cff..14f8a92 100644
> >>--- a/drivers/watchdog/watchdog_dev.c
> >>+++ b/drivers/watchdog/watchdog_dev.c
> >>@@ -92,9 +92,13 @@ static inline bool watchdog_need_worker(struct 
> >>watchdog_device *wdd)
> >>  	 *   thus is aware that the framework supports generating heartbeat
> >>  	 *   requests.
> >>  	 * - Userspace requests a longer timeout than the hardware can 
> >>  	 handle.
> >>+	 *
> >>+	 * Alternatively, if userspace has not opened the watchdog
> >>+	 * device, we take care of feeding the watchdog if it is
> >>+	 * running.
> >>  	 */
> >>-	return hm && ((watchdog_active(wdd) && t > hm) ||
> >>-		      (t && !watchdog_active(wdd) && 
> >>watchdog_hw_running(wdd)));
> >>+	return (hm && watchdog_active(wdd) && t > hm) ||
> >>+		(t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
> >>  }
> >>
> >>  static long watchdog_next_keepalive(struct watchdog_device *wdd)
> >>@@ -107,7 +111,7 @@ static long watchdog_next_keepalive(struct 
> >>watchdog_device *wdd)
> >>  	unsigned int hw_heartbeat_ms;
> >>
> >>  	virt_timeout = wd_data->last_keepalive + 
> >>  	msecs_to_jiffies(timeout_ms);
> >>-	hw_heartbeat_ms = min(timeout_ms, wdd->max_hw_heartbeat_ms);
> >>+	hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
> >>  	keepalive_interval = msecs_to_jiffies(hw_heartbeat_ms / 2);
> >>
> >>  	if (!watchdog_active(wdd))
> >>--
> >>2.5.0
> >>
> >
> >Kind regards,
> >Wim.
> >
> >
> 

Kind regards,
Wim.