Messages in this thread | | | Date | Mon, 8 Nov 2010 19:05:23 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v2] watchdog: touch_nmi_watchdog should only touch local cpu not every one |
| |
On Mon, Nov 08, 2010 at 11:44:35AM -0500, Don Zickus wrote: > I ran into a scenario where while one cpu was stuck and should have panic'd > because of the NMI watchdog, it didn't. The reason was another cpu was spewing > stack dumps on to the console. Upon investigation, I noticed that when writing > to the console and also when dumping the stack, the watchdog is touched. > > This causes all the cpus to reset their NMI watchdog flags and the 'stuck' cpu > just spins forever. > > This change causes the semantics of touch_nmi_watchdog to be changed slightly. > Previously, I accidentally changed the semantics and we noticed there was a > codepath in which touch_nmi_watchdog could be touched from a preemtible area. > That caused a BUG() to happen when CONFIG_DEBUG_PREEMPT was enabled. I believe > it was the acpi code. > > My attempt here re-introduces the change to have the touch_nmi_watchdog() code > only touch the local cpu instead of all of the cpus. But instead of using > __get_cpu_var(), I use the __raw_get_cpu_var() version. > > This avoids the preemption problem. However my reasoning wasn't because I was > trying to be lazy. Instead I rationalized it as, well if preemption is enabled > then interrupts should be enabled to and the NMI watchdog will have no reason > to trigger. So it won't matter if the wrong cpu is touched because the percpu > interrupt counters the NMI watchdog uses should still be incrementing. > > V2: remove touch_all_nmi_watchdog code
Are you sure you did? :)
> +void touch_all_nmi_watchdogs(void) > +{ > if (watchdog_enabled) { > unsigned cpu; > > @@ -151,7 +166,7 @@ void touch_nmi_watchdog(void) > } > touch_softlockup_watchdog(); > } > -EXPORT_SYMBOL(touch_nmi_watchdog); > +EXPORT_SYMBOL(touch_all_nmi_watchdogs); > > #endif > > -- > 1.7.2.3 >
| |