On 01/14/14 at 04:41pm, Dave Young wrote:
> On 01/14/14 at 09:26am, Wim Van Sebroeck wrote:
> > Hi Dave,
> >
> > > In kdump kernel watchdog could interrupt vmcore capturing because we
> > > have no way to disable/stop it while crashing happens.
> > >
> > > Add a module parameter stop_before_register so watchdog can be stopped
> > > before register in driver loading path. Thus we can try to load the
> > > watchdog driver as early as possible in kdump kernel to ensure vmcore
> > > capturing.
> > >
> > > Don Zickus mentioned that there's the case that bios start the watchdog
> > > and it is expected that the kernel keep the watchdog alive. To address
> > > this case I added the module parameter which is false by default so
> > > it will stop the watchdog only when user provice kernel cmdline
> > > "watchdog.stop_before_register=1".
> > >
> > > Signed-off-by: Dave Young <dyoung@xxxxxxxxxx>
> > > ---
> > > drivers/watchdog/watchdog_core.c | 6 ++++++
> > > 1 file changed, 6 insertions(+)
> > >
> > > --- linux.orig/drivers/watchdog/watchdog_core.c
> > > +++ linux/drivers/watchdog/watchdog_core.c
> > > @@ -42,6 +42,7 @@
> > >
> > > static DEFINE_IDA(watchdog_ida);
> > > static struct class *watchdog_class;
> > > +static bool stop_before_register;
> > >
> > > static void watchdog_check_min_max_timeout(struct watchdog_device *wdd)
> > > {
> > > @@ -119,6 +120,9 @@ int watchdog_register_device(struct watc
> > > if (wdd->ops->start == NULL || wdd->ops->stop == NULL)
> > > return -EINVAL;
> > >
> > > + if (stop_before_register)
> > > + wdd->ops->stop(wdd);
> > > +
> > > watchdog_check_min_max_timeout(wdd);
> > >
> > > /*
> > > @@ -220,6 +224,8 @@ static void __exit watchdog_exit(void)
> > > subsys_initcall(watchdog_init);
> > > module_exit(watchdog_exit);
> > >
> > > +module_param(stop_before_register, bool, 0644);
> > > +
> > > MODULE_AUTHOR("Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>");
> > > MODULE_AUTHOR("Wim Van Sebroeck <wim@xxxxxxxxx>");
> > > MODULE_DESCRIPTION("WatchDog Timer Driver Core");
> >
> > Hmm, need to look closer to this, but my first thought is:
> > what about devices that cannot be stopped once started...
> > They should be able to override this module_parameter...
>
> Hi, Wim
>
> Thanks for quick feedback!
>
> I'm not sure the meaning of "cannot be stopped", if it means that
> the policy that it should not be stopped, I think since the watchdog_core
> is always built-in so the param can only be provided via boot cmdline it would
> be fine?
Hmm, the wdt driver can be removed then insmod again.
I think you are talking about the nowayout, for this case probably should add below:
if (stop_before_register && !nowayout)
stop it.
But is there a general way for checkout nowayout, could you give some
hints?
>
> For device which really *cannot* stop, the stop() will fail silently?
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