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Date: Sat, 14 Jan 2017 09:33:10 +0800 From: qiaonuohan <qiaonuohan@...wei.com> To: Zhou Chengming <zhouchengming1@...wei.com>, <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>, <x86@...nel.org>, <peterz@...radead.org>, <ak@...ux.intel.com>, <eranian@...gle.com>, <kan.liang@...el.com>, <davidcc@...gle.com>, <dave.hansen@...ux.intel.com>, <linux-kernel@...r.kernel.org> CC: <guohanjun@...wei.com> Subject: Re: [PATCH] fix race caused by hyperthreads when online an offline cpu ping... On 2017/1/12 17:32, Zhou Chengming wrote: > After online an offline cpu, cpu_hw_events.excl_thread_id will always be > set to 1 in intel_pmu_cpu_starting() even when its sibling's excl_thread_id > is also 1. Then the two siblings will use the same state in their shared > hw_hw_events.excl_cntrs, it will cause race problem. > > The race senario is like this: > > Two cpu (7 and 19) are siblings, excl_thread_id of 7 and 19 are 0 and 1. > After offline and online cpu 7, intel_pmu_cpu_starting() will set excl_thread_id > of cpu 7 to 1. Then both cpu 7 and 19 will use the same state in their > shared hw_hw_events.excl_cntrs. > > cpu7 cpu19 > --- --- > intel_start_scheduling() > set state->sched_started = true > intel_put_excl_constraints() { > if (!state->sched_started) > spin_lock // not executed > intel_stop_scheduling() > set state->sched_started = false > if (!state->sched_started) > spin_unlock // excuted > > Signed-off-by: NuoHan Qiao <qiaonuohan@...wei.com> > Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com> > --- > arch/x86/events/intel/core.c | 7 +++++-- > 1 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c > index a74a2db..593d8c9 100644 > --- a/arch/x86/events/intel/core.c > +++ b/arch/x86/events/intel/core.c > @@ -3164,13 +3164,16 @@ static void intel_pmu_cpu_starting(int cpu) > > if (x86_pmu.flags & PMU_FL_EXCL_CNTRS) { > for_each_cpu(i, topology_sibling_cpumask(cpu)) { > + struct cpu_hw_events *sibling; > struct intel_excl_cntrs *c; > > - c = per_cpu(cpu_hw_events, i).excl_cntrs; > + sibling = &per_cpu(cpu_hw_events, i); > + c = sibling->excl_cntrs; > if (c && c->core_id == core_id) { > cpuc->kfree_on_online[1] = cpuc->excl_cntrs; > cpuc->excl_cntrs = c; > - cpuc->excl_thread_id = 1; > + if (!sibling->excl_thread_id) > + cpuc->excl_thread_id = 1; > break; > } > } >
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