diff options
| -rw-r--r-- | arch/x86/events/core.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index e07b36c5588a..183a972f9210 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2109,6 +2109,18 @@ static void x86_pmu_event_mapped(struct perf_event *event) if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) return; + /* + * This function relies on not being called concurrently in two + * tasks in the same mm. Otherwise one task could observe + * perf_rdpmc_allowed > 1 and return all the way back to + * userspace with CR4.PCE clear while another task is still + * doing on_each_cpu_mask() to propagate CR4.PCE. + * + * For now, this can't happen because all callers hold mmap_sem + * for write. If this changes, we'll need a different solution. + */ + lockdep_assert_held_exclusive(¤t->mm->mmap_sem); + if (atomic_inc_return(¤t->mm->context.perf_rdpmc_allowed) == 1) on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1); } |