Re: [PATCH] fix race caused by hyperthreads when online an offline cpu

[qiaonuohan <qiaonuohan@huawei.com>]

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@huawei.com>
> Signed-off-by: Zhou Chengming <zhouchengming1@huawei.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;
>  			}
>  		}
>