On Mon, Mar 30, 2015 at 02:51:05PM -0400, [email protected] wrote: > From: Chris Metcalf <[email protected]> > > Running watchdog can be a helpful debugging feature on regular > cores, but it's incompatible with nohz_full, since it forces > regular scheduling events. Accordingly, just exit out immediately > from any nohz_full core. > > An alternate approach would be to add a flags field or function to > smp_hotplug_thread to control on which cores the percpu threads > are created, but it wasn't clear that much mechanism was useful.
Hi Chris, It seems like the correct solution would be to hook into the idle_loop somehow. If the cpu is idle, then it seems unlikely that a lockup could occur. My fear with this apporach is a lockup would occur on the nohz cpu and it would go undetected because that cpu is disabled. Further no printk is thrown out to even indicate a cpu is disabled making it more difficult to debug. Cheers, Don > > Signed-off-by: Chris Metcalf <[email protected]> > --- > kernel/watchdog.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 3174bf8e3538..8a46d9d8a66f 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -19,6 +19,7 @@ > #include <linux/sysctl.h> > #include <linux/smpboot.h> > #include <linux/sched/rt.h> > +#include <linux/tick.h> > > #include <asm/irq_regs.h> > #include <linux/kvm_para.h> > @@ -431,6 +432,10 @@ static void watchdog_enable(unsigned int cpu) > hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); > hrtimer->function = watchdog_timer_fn; > > + /* nohz_full cpus do not do watchdog checking. */ > + if (tick_nohz_full_cpu(cpu)) > + do_exit(0); > + > /* Enable the perf event */ > watchdog_nmi_enable(cpu); > > -- > 2.1.2 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
