Messages in this thread Patch in this message | | | Date | Tue, 08 Sep 2015 06:47:26 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH v3 2/9] watchdog: Introduce hardware maximum timeout in watchdog core |
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Hi Uwe,
On 09/08/2015 03:33 AM, Uwe Kleine-König wrote: > Hello, >
>> [...] >> +static long watchdog_next_keepalive(struct watchdog_device *wdd) >> +{ >> + unsigned int hw_timeout_ms = wdd->timeout * 1000; >> + unsigned long keepalive_interval; >> + unsigned long last_heartbeat; >> + unsigned long virt_timeout; >> + >> + virt_timeout = wdd->last_keepalive + msecs_to_jiffies(hw_timeout_ms); > > Just looking at this line this is wrong. It just happens to be correct > here because hw_timeout_ms non-intuitively is set to wdd->timeout * 1000 > which might not reflect what is programmed into the hardware. > I don't see where the code is wrong. Sure, the variable name doesn't match its initial use, but that doesn't make it wrong. I can pick a different variable name if that helps (any suggested name ?).
> I'd write: > > virt_timeout = wdd->last_keepalive + msecs_to_jiffies(wdd->timeout * 1000); > > ... > >> + if (hw_timeout_ms > wdd->max_hw_timeout_ms) >> + hw_timeout_ms = wdd->max_hw_timeout_ms; > > hw_timeout_ms = min(wdd->timeout * 1000, wdd->max_hw_timeout_ms); >
The reason for writing the code as is was to avoid the double 'wdd->timeout * 1000' (and to avoid a line > 80 columns in the first line).
>> [...] >> @@ -61,26 +143,27 @@ static struct watchdog_device *old_wdd; >> >> static int watchdog_ping(struct watchdog_device *wdd) >> { >> - int err = 0; >> + int err; >> >> mutex_lock(&wdd->lock); >> + wdd->last_keepalive = jiffies; >> + err = _watchdog_ping(wdd); >> + watchdog_update_worker(wdd, false); > > Here the cancel argument could also be true, right? That's because after > a ping (that doesn't modify the timeout) the result of > watchdog_need_worker doesn't change and so either the worker isn't > running + stopping it again doesn't hurt, or the timer is running and so > it's not tried to be stopped. > Could, but it isn't necessary.
>> + mutex_unlock(&wdd->lock); >> >> - if (test_bit(WDOG_UNREGISTERED, &wdd->status)) { >> - err = -ENODEV; >> - goto out_ping; >> - } >> + return err; >> +} >> >> - if (!watchdog_active(wdd)) >> - goto out_ping; >> +static void watchdog_ping_work(struct work_struct *work) >> +{ >> + struct watchdog_device *wdd; >> >> - if (wdd->ops->ping) >> - err = wdd->ops->ping(wdd); /* ping the watchdog */ >> - else >> - err = wdd->ops->start(wdd); /* restart watchdog */ >> + wdd = container_of(to_delayed_work(work), struct watchdog_device, work); >> >> -out_ping: >> + mutex_lock(&wdd->lock); >> + _watchdog_ping(wdd); >> + watchdog_update_worker(wdd, false); > > Here for the same reason you could pass true. So there is no caller that > needs to pass false which allows to simplify the function. (i.e. drop > the cancel parameter and simplify it assuming cancel is true) >
There will be another call with 'false' added with a later patch, though that could live with 'true'.
The function is executed by the worker, and since it is already executing canceling it would not be necessary.
I don't know what happens if an attempt is made to cancel a worker from its work function. I seem to recall that it causes a stall, but I may be wrong. Any idea ?
>> mutex_unlock(&wdd->lock); >> - return err; >> } >> >> /* >> [...] >> @@ -119,8 +134,9 @@ static inline void watchdog_set_nowayout(struct watchdog_device *wdd, bool noway >> /* Use the following function to check if a timeout value is invalid */ >> static inline bool watchdog_timeout_invalid(struct watchdog_device *wdd, unsigned int t) >> { >> - return ((wdd->max_timeout != 0) && >> - (t < wdd->min_timeout || t > wdd->max_timeout)); > > Is this (old) code correct? watchdog_timeout_invalid returns false if > wdd->max_timeout == 0 && t < wdd->min_timeout. I would have expected: > > return (wdd->max_timeout != 0 && t > wdd->max_timeout) || > t < wdd->min_timeout; > You are correct. However, that is a different problem, which I addressed in 'watchdog: Always evaluate new timeout against min_timeout'.
>> + return t > UINT_MAX / 1000 || >> + (!wdd->max_hw_timeout_ms && wdd->max_timeout && >> + (t < wdd->min_timeout || t > wdd->max_timeout)); > > So should this better be: > > /* internal calculation is done in ms using unsigned variables */ > if (t > UINT_MAX / 1000) > return 1; > > /* > * compat code for drivers not being aware of framework pings to > * bridge timeouts longer than supported by the hardware. > */ > if (!wdd->max_hw_timeout && wdd->max_timeout && t > wdd->max_timeout) > return 1; > > if (t < wdd->min_timeout) > return 1; >
After all patches are applied, my code is
/* Use the following function to check if a timeout value is invalid */ static inline bool watchdog_timeout_invalid(struct watchdog_device *wdd, unsigned int t) { return t > UINT_MAX / 1000 || t < wdd->min_timeout || (!wdd->max_hw_timeout_ms && wdd->max_timeout && t > wdd->max_timeout); }
which is exactly the same (without the comments).
Thanks, Guenter
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