Messages in this thread | | | Date | Mon, 13 Sep 2010 10:08:13 +0200 | From | Heiko Carstens <> | Subject | Re: [PATCH] generic-ipi: fix deadlock in __smp_call_function_single |
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On Sat, Sep 11, 2010 at 09:42:16AM -0700, Venkatesh Pallipadi wrote: > On Sat, Sep 11, 2010 at 2:20 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Fri, 2010-09-10 at 17:28 -0700, Andrew Morton wrote: > >> Where is this scheduler bug? Did it occur because someone didn't > >> understand __smp_call_function_single()? Or did it occur because the > >> scheduler code is doing something which its implementors did not expect > >> or intend? > > > > > > It comes from 83cd4fe2 (sched: Change nohz idle load balancing logic to > > push model), where nohz_balance_kick() simply needs to kick the > > designated driver into action. > > > > I take it Venki assumed __smp_call_function_single() works like > > smp_call_function_single() where you can use it for the local cpu as > > well. > > Yes. This was an oversight while moving from using send_remote_softirq > to using __smp_call_function_single. > Also, as we don't have rq lock around this point, it seems possible > that the CPU that was busy and wants to kick idle load balance on > remote CPU, could have become idle and nominated itself as idle load > balancer. > > Below patch looks good to me. > > Acked-by: Venkatesh Pallipadi <venki@google.com> > > I guess, we also need a WARN_ON_ONCE for (cpu == smp_processor_id()) > in __smp_call_function_single(), as the eventual result of this bug > that Heiko saw was a deadlock
Either that or my generic IPI patch should be applied. At least to me it was rather surprising to see that smp_call_function_single() and __smp_call_function_single() behave differently when the 'remote' cpu is the current cpu. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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