1 files changed, 14 insertions, 1 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cb8744a1b120..e76e4959908c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -761,8 +761,18 @@ perf_lock_task_context(struct task_struct *task, int ctxn, unsigned long *flags)
 {
         struct perf_event_context *ctx;
 
-        rcu_read_lock();
 retry:
+        /*
+         * One of the few rules of preemptible RCU is that one cannot do
+         * rcu_read_unlock() while holding a scheduler (or nested) lock when
+         * part of the read side critical section was preemptible -- see
+         * rcu_read_unlock_special().
+         *
+         * Since ctx->lock nests under rq->lock we must ensure the entire read
+         * side critical section is non-preemptible.
+         */
+        preempt_disable();
+        rcu_read_lock();
         ctx = rcu_dereference(task->perf_event_ctxp[ctxn]);
         if (ctx) {
                 /*
@@ -778,6 +788,8 @@ retry:
                 raw_spin_lock_irqsave(&ctx->lock, *flags);
                 if (ctx != rcu_dereference(task->perf_event_ctxp[ctxn])) {
                         raw_spin_unlock_irqrestore(&ctx->lock, *flags);
+                        rcu_read_unlock();
+                        preempt_enable();
                         goto retry;
                 }
 
@@ -787,6 +799,7 @@ retry:
                 }
         }
         rcu_read_unlock();
+        preempt_enable();
         return ctx;
 }