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(&current->mm->mmap_sem);
+
         if (atomic_inc_return(&current->mm->context.perf_rdpmc_allowed) == 1)
                 on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1);
 }