1 files changed, 40 insertions, 0 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 65349f07b878..66677003e223 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -71,6 +71,46 @@ void user_enter(void)
         local_irq_restore(flags);
 }
 
+#ifdef CONFIG_PREEMPT
+/**
+ * preempt_schedule_context - preempt_schedule called by tracing
+ *
+ * The tracing infrastructure uses preempt_enable_notrace to prevent
+ * recursion and tracing preempt enabling caused by the tracing
+ * infrastructure itself. But as tracing can happen in areas coming
+ * from userspace or just about to enter userspace, a preempt enable
+ * can occur before user_exit() is called. This will cause the scheduler
+ * to be called when the system is still in usermode.
+ *
+ * To prevent this, the preempt_enable_notrace will use this function
+ * instead of preempt_schedule() to exit user context if needed before
+ * calling the scheduler.
+ */
+void __sched notrace preempt_schedule_context(void)
+{
+        struct thread_info *ti = current_thread_info();
+        enum ctx_state prev_ctx;
+
+        if (likely(ti->preempt_count || irqs_disabled()))
+                return;
+
+        /*
+         * Need to disable preemption in case user_exit() is traced
+         * and the tracer calls preempt_enable_notrace() causing
+         * an infinite recursion.
+         */
+        preempt_disable_notrace();
+        prev_ctx = exception_enter();
+        preempt_enable_no_resched_notrace();
+
+        preempt_schedule();
+
+        preempt_disable_notrace();
+        exception_exit(prev_ctx);
+        preempt_enable_notrace();
+}
+EXPORT_SYMBOL_GPL(preempt_schedule_context);
+#endif /* CONFIG_PREEMPT */
 
 /**
  * user_exit - Inform the context tracking that the CPU is