On Wed, Feb 04, 2015 at 11:14:55PM -0800, Dave Hansen wrote: > On 02/04/2015 05:53 PM, Sedat Dilek wrote: > > The architecture-specific switch_mm() function can be called by offline > > CPUs, but includes event tracing, which cannot be legally carried out > > on offline CPUs. This results in a lockdep-RCU splat. This commit fixes > > this splat by omitting the tracing when the CPU is offline. > ... > >>> >> > load_cr3(next->pgd); > >>> >> > - trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); > >>> >> > + if (cpu_online(smp_processor_id())) > >>> >> > + trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); > > Is this, perhaps, something that we should be doing in the generic trace > code so that all of the trace users don't have to worry about it? Also, > this patch will add overhead to the code when tracing is off. It would > be best if we could manage to make the cpu_online() check only in the > cases where the tracepoint is on. I considered doing this in the _rcuidle piece of the trace code, but unlike the RCU idle exit/entry in the _rcuidle stuff, the work required to get through the RCU online/offline code is pretty heavyweight. You end up having 16 CPUs contending for an rcu_node lock, for example. But maybe you are instead suggesting pushing only the cpu_online() check into the trace infrastructure. If so, fair point, and I will take a look at this. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
