On 05/15/2015 06:57 PM, Shreyas B. Prabhu wrote: > trace_mm_page_pcpu_drain, trace_kmem_cache_free, trace_mm_page_free > can be potentially called from an offlined cpu. Since trace points use > RCU and RCU should not be used from offlined cpus, we have checks to > filter out such calls. > > But these checks use smp_processor_id() and since these trace calls can > happen from preemptable sections, this throws a warning when running > with CONFIG_DEBUG_PREEMPT set. > > Now consider task gets migrated after calling smp_processor_id() > - From an online cpu to another online cpu - No impact > - From an online cpu to an offline cpu - Should never happen > - From an offline cpu to an online cpu - Once a cpu has been > offlined it returns to cpu_idle_loop, discovers its offline and calls > arch_cpu_idle_dead. All this happens with preemption disabled. So > this scenario too should never happen. > > Thus running with PREEMPT set has no impact on the condition. So use > raw_smp_processor_id() so that the warnings are suppressed. > > Signed-off-by: Shreyas B. Prabhu <[email protected]> > --- > include/trace/events/kmem.h | 34 +++++++++++++++++++++++++++++++--- > 1 file changed, 31 insertions(+), 3 deletions(-) > > diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h > index 6cd975f..f7554fd 100644 > --- a/include/trace/events/kmem.h > +++ b/include/trace/events/kmem.h > @@ -146,7 +146,16 @@ DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free, > > TP_ARGS(call_site, ptr), > > - TP_CONDITION(cpu_online(smp_processor_id())) > + /* > + * This trace can be potentially called from an offlined cpu. > + * Since trace points use RCU and RCU should not be used from > + * offline cpus, filter such calls out. > + * While this trace can be called from a preemptable section, > + * it has no impact on the condition since tasks can migrate > + * only from online cpus to other online cpus. Thus its safe > + * to use raw_smp_processor_id. > + */ > + TP_CONDITION(cpu_online(raw_smp_processor_id())) > ); > > TRACE_EVENT_CONDITION(mm_page_free, > @@ -155,7 +164,17 @@ TRACE_EVENT_CONDITION(mm_page_free, > > TP_ARGS(page, order), > > - TP_CONDITION(cpu_online(smp_processor_id())), > + > + /* > + * This trace can be potentially called from an offlined cpu. > + * Since trace points use RCU and RCU should not be used from > + * offline cpus, filter such calls out. > + * While this trace can be called from a preemptable section, > + * it has no impact on the condition since tasks can migrate > + * only from online cpus to other online cpus. Thus its safe > + * to use raw_smp_processor_id. > + */ > + TP_CONDITION(cpu_online(raw_smp_processor_id())), > > TP_STRUCT__entry( > __field( unsigned long, pfn ) > @@ -263,7 +282,16 @@ TRACE_EVENT_CONDITION(mm_page_pcpu_drain, > > TP_ARGS(page, order, migratetype), > > - TP_CONDITION(cpu_online(smp_processor_id())), > + /* > + * This trace can be potentially called from an offlined cpu. > + * Since trace points use RCU and RCU should not be used from > + * offline cpus, filter such calls out. > + * While this trace can be called from a preemptable section, > + * it has no impact on the condition since tasks can migrate > + * only from online cpus to other online cpus. Thus its safe > + * to use raw_smp_processor_id. > + */ > + TP_CONDITION(cpu_online(raw_smp_processor_id())), > > TP_STRUCT__entry( > __field( unsigned long, pfn )
Reviewed-by: Preeti U Murthy <[email protected]> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
