1 files changed, 61 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b001c133c359..589e7308c615 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4614,6 +4614,67 @@ need_resched:
 }
 EXPORT_SYMBOL(schedule);
 
+#ifdef CONFIG_SMP
+/*
+ * Look out! "owner" is an entirely speculative pointer
+ * access and not reliable.
+ */
+int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
+{
+        unsigned int cpu;
+        struct rq *rq;
+
+        if (!sched_feat(OWNER_SPIN))
+                return 0;
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+        /*
+         * Need to access the cpu field knowing that
+         * DEBUG_PAGEALLOC could have unmapped it if
+         * the mutex owner just released it and exited.
+         */
+        if (probe_kernel_address(&owner->cpu, cpu))
+                goto out;
+#else
+        cpu = owner->cpu;
+#endif
+
+        /*
+         * Even if the access succeeded (likely case),
+         * the cpu field may no longer be valid.
+         */
+        if (cpu >= nr_cpumask_bits)
+                goto out;
+
+        /*
+         * We need to validate that we can do a
+         * get_cpu() and that we have the percpu area.
+         */
+        if (!cpu_online(cpu))
+                goto out;
+
+        rq = cpu_rq(cpu);
+
+        for (;;) {
+                /*
+                 * Owner changed, break to re-assess state.
+                 */
+                if (lock->owner != owner)
+                        break;
+
+                /*
+                 * Is that owner really running on that cpu?
+                 */
+                if (task_thread_info(rq->curr) != owner || need_resched())
+                        return 0;
+
+                cpu_relax();
+        }
+out:
+        return 1;
+}
+#endif
+
 #ifdef CONFIG_PREEMPT
 /*
  * this is the entry point to schedule() from in-kernel preemption