Merge branch 'timers/posix-cpu-timers-for-tglx' of

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/core

Frederic sayed: "Most of these patches have been hanging around for
several month now, in -mmotm for a significant chunk. They already
missed a few releases."

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 40 insertions, 1 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 65349f07b878..383f8231e436 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -15,7 +15,6 @@
  */
 
 #include <linux/context_tracking.h>
-#include <linux/kvm_host.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 #include <linux/hardirq.h>
@@ -71,6 +70,46 @@ 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