lkml.org 
[lkml]   [2010]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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
>



\
 
 \ /
  Last update: 2010-11-08 19:07    [W:0.055 / U:0.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site