Re: [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector_reconfigure
On 24/06/2022, 11:37:23, Christoph Hellwig wrote: > On Tue, Jun 14, 2022 at 03:54:12PM +0200, Laurent Dufour wrote: >> The watchdog_mutex is exported to allow some variable to be changed under >> its protection and prevent any conflict. >> The lockup_detector_reconfigure() function is exported and is expected to >> be called under the protection of watchdog_mutex. > > Please provide an actual function accessor instead of directly touching > a global lock. Thanks Christoph, I'll try to not touch to that mutex, if that's not doable, I'll create function accessor as you're suggesting.
Re: [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector_reconfigure
On Tue, Jun 14, 2022 at 03:54:12PM +0200, Laurent Dufour wrote: > The watchdog_mutex is exported to allow some variable to be changed under > its protection and prevent any conflict. > The lockup_detector_reconfigure() function is exported and is expected to > be called under the protection of watchdog_mutex. Please provide an actual function accessor instead of directly touching a global lock.
Re: [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector_reconfigure
On 24/06/2022, 08:31:55, Michael Ellerman wrote: > Laurent Dufour writes: >> In some cricunstances it may be interesting to reconfigure the watchdog >> from inside the kernel. >> >> On PowerPC, this may helpful before and after a LPAR migration (LPM) is >> initiated, because it implies some latencies, watchdog, and especially NMI >> watchdog is expected to be triggered during this operation. Reconfiguring >> the watchdog, would prevent it to happen too frequently during LPM. >> >> The watchdog_mutex is exported to allow some variable to be changed under >> its protection and prevent any conflict. >> The lockup_detector_reconfigure() function is exported and is expected to >> be called under the protection of watchdog_mutex. >> >> Signed-off-by: Laurent Dufour >> --- >> include/linux/nmi.h | 3 +++ >> kernel/watchdog.c | 6 +++--- >> 2 files changed, 6 insertions(+), 3 deletions(-) > > Is there a maintainer for kernel/watchdog.c ? Nothing clearly identified AFAICT. I'll add the commit signers reported by get_maintainer.pl. > There's Wim & Guenter at linux-watchdog@vger but I think that's only for > drivers/watchdog? > > Maybe we should Cc that list anyway? Yes, that's a good idea. > > >> diff --git a/include/linux/nmi.h b/include/linux/nmi.h >> index 750c7f395ca9..84300fb0f90a 100644 >> --- a/include/linux/nmi.h >> +++ b/include/linux/nmi.h >> @@ -122,6 +122,9 @@ int watchdog_nmi_probe(void); >> int watchdog_nmi_enable(unsigned int cpu); >> void watchdog_nmi_disable(unsigned int cpu); >> >> +extern struct mutex watchdog_mutex; >> +void lockup_detector_reconfigure(void); > > It would be preferable if we didn't export the mutex. > > I think you could arrange that by ... > > Renaming lockup_detector_configure() to __lockup_detector_configure() > and then adding a new lockup_detector_configure() that is non-static and > takes the lock around __lockup_detector_configure(). Unfortunately, that will not be enough, because this mutex is also used to protect wd_watchdog, to ensure it is not changed while another operation is in progress. I may try finding another way to protect that value, may be using WRITE/READ_ONCE(). Indeed, the only requirement is to read a stable value in watchdog_calc_timeouts(). Thanks, Laurent.
Re: [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector_reconfigure
Laurent Dufour writes: > In some cricunstances it may be interesting to reconfigure the watchdog > from inside the kernel. > > On PowerPC, this may helpful before and after a LPAR migration (LPM) is > initiated, because it implies some latencies, watchdog, and especially NMI > watchdog is expected to be triggered during this operation. Reconfiguring > the watchdog, would prevent it to happen too frequently during LPM. > > The watchdog_mutex is exported to allow some variable to be changed under > its protection and prevent any conflict. > The lockup_detector_reconfigure() function is exported and is expected to > be called under the protection of watchdog_mutex. > > Signed-off-by: Laurent Dufour > --- > include/linux/nmi.h | 3 +++ > kernel/watchdog.c | 6 +++--- > 2 files changed, 6 insertions(+), 3 deletions(-) Is there a maintainer for kernel/watchdog.c ? There's Wim & Guenter at linux-watchdog@vger but I think that's only for drivers/watchdog? Maybe we should Cc that list anyway? > diff --git a/include/linux/nmi.h b/include/linux/nmi.h > index 750c7f395ca9..84300fb0f90a 100644 > --- a/include/linux/nmi.h > +++ b/include/linux/nmi.h > @@ -122,6 +122,9 @@ int watchdog_nmi_probe(void); > int watchdog_nmi_enable(unsigned int cpu); > void watchdog_nmi_disable(unsigned int cpu); > > +extern struct mutex watchdog_mutex; > +void lockup_detector_reconfigure(void); It would be preferable if we didn't export the mutex. I think you could arrange that by ... Renaming lockup_detector_configure() to __lockup_detector_configure() and then adding a new lockup_detector_configure() that is non-static and takes the lock around __lockup_detector_configure(). cheers
