Messages in this thread | | | Date | Mon, 11 Aug 2008 22:06:28 -0400 | From | Gregory Haskins <> | Subject | Re: [PATCH] BUG: using smp_processor_id() in preemptible [00000000] code: caller is __qdisc_run |
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Steven Rostedt wrote: > On Mon, 11 Aug 2008, David Miller wrote: > > >> From: Peter Zijlstra <a.p.zijlstra@chello.nl> >> Date: Mon, 11 Aug 2008 23:09:38 +0200 >> >> >>> On Mon, 2008-08-11 at 14:00 -0700, David Miller wrote: >>> >>>> From: "John Kacur" <jkacur@gmail.com> >>>> Date: Mon, 11 Aug 2008 15:11:46 +0200 >>>> >>>> >>>>> __qdisc_run() calls qdisc_restart() which calls >>>>> handle_dev_cpu_collision(skb, dev, q); and then the problem shows up >>>>> here: >>>>> __get_cpu_var(netdev_rx_stat).cpu_collision++; >>>>> >>>>> The solution is to disable interrupts around the above increment. Here >>>>> is an attached patch to do so. (Thank's to Peter Zijlstra for help in >>>>> the analysis and dropping the answer in my lap, so if I got it right >>>>> it is due to his help, but if I messed it up, then I did that part all >>>>> by myself.) >>>>> >>>> __qdisc_run() always runs in software interrupt context, >>>> so I guess this is some problem with the -rt stuff running >>>> software interrupts in threads? >>>> >>> Hmm, good point - and those threads should be cpu affine on -rt if I'm >>> not mistaken. Steven, do you happen to remember details? >>> >> The key issue is whether those threads run software interrupts >> in a compatible environment. And such a proper environment allows >> plain smp_processor_id() without any special preparations. >> >> > > Yes, we have a softirq thread per CPU. We should have a test in the > smp_processor_id for rt to not bug if it is called by known "per_cpu" > threads. > something like
#ifdef CONFIG_PREEMPT_RT WARN_ON(!in_atomic() && current->rt.nr_cpus_allowed > 1); #else WARN_ON(!in_atomic()); #endif
would probably work and be fairly efficient. Of course nr_cpus_allowed technically could be adjusted at any time, so perhaps not. Its probably good enough for a warning check, however.
> -- Steve > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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