2 files changed, 57 insertions, 1 deletions

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 87a03c746f17..f5d4723cdb3d 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -33,9 +33,25 @@ do { \
                 preempt_schedule(); \
 } while (0)
 
+#ifdef CONFIG_CONTEXT_TRACKING
+
+void preempt_schedule_context(void);
+
+#define preempt_check_resched_context() \
+do { \
+        if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
+                preempt_schedule_context(); \
+} while (0)
+#else
+
+#define preempt_check_resched_context() preempt_check_resched()
+
+#endif /* CONFIG_CONTEXT_TRACKING */
+
 #else /* !CONFIG_PREEMPT */
 
 #define preempt_check_resched()         do { } while (0)
+#define preempt_check_resched_context() do { } while (0)
 
 #endif /* CONFIG_PREEMPT */
 
@@ -88,7 +104,7 @@ do { \
 do { \
         preempt_enable_no_resched_notrace(); \
         barrier(); \
-        preempt_check_resched(); \
+        preempt_check_resched_context(); \
 } while (0)
 
 #else /* !CONFIG_PREEMPT_COUNT */
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