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. > > Signed-off-by: Rasmus Villemoes <rasmus.villem...@prevas.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.
