Messages in this thread | | | Date | Fri, 16 Apr 2010 17:32:12 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v2] [watchdog] combine nmi_watchdog and softlockup |
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On Fri, Apr 16, 2010 at 11:04:07AM -0400, Don Zickus wrote: > > This is really just a corner case, I guess you don't need to > > bother with that. It is actually racy against other cpus and adding > > a spinlock here (in the everything is fine path) would be an overkill. > > > > In fact, having two per cpu vars named hardlockup_warned and > > softlockup_warned would be better than cpumasks. I'm sorry I > > suggested you the cpumask, but such per cpu vars will avoid > > you dealing with these synchonization issues. And one of the primary > > rules is usually to never take a lock from NMIs if we can :) > > Yeah, I guess per cpu is better. I agree that locks in NMI are frowned > upon but I wasn't sure of it was dealt with.
They work in fact. They are just not checked by lockdep. And mostly they are very dangerous: if something else can take it (from interrupt, from context) then this is a deadlock. And even though we ensure this is only taken from NMI, we tend to avoid that.
> I'll try to implement this. Any objections if I combined hardlockup and > softlockup with per cpu watchdog_warn and have bit masks for HARDLOCKUP > and SOFTLOCKUP? I hate to just waste per cpu space for this.
Hmm, a hardlockup can come in after a softlockup. Don't worry too much about memory: usually the more you have cpu, the more you have memory :) Plus this is debugging code, not something supposed to be enabled in production.
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