1 files changed, 83 insertions, 0 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
new file mode 100644
index 000000000000..e0e07fd55508
--- /dev/null
+++ b/kernel/context_tracking.c
@@ -0,0 +1,83 @@
+#include <linux/context_tracking.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/percpu.h>
+#include <linux/hardirq.h>
+
+struct context_tracking {
+        /*
+         * When active is false, hooks are not set to
+         * minimize overhead: TIF flags are cleared
+         * and calls to user_enter/exit are ignored. This
+         * may be further optimized using static keys.
+         */
+        bool active;
+        enum {
+                IN_KERNEL = 0,
+                IN_USER,
+        } state;
+};
+
+static DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
+#ifdef CONFIG_CONTEXT_TRACKING_FORCE
+        .active = true,
+#endif
+};
+
+void user_enter(void)
+{
+        unsigned long flags;
+
+        /*
+         * Some contexts may involve an exception occuring in an irq,
+         * leading to that nesting:
+         * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
+         * This would mess up the dyntick_nesting count though. And rcu_irq_*()
+         * helpers are enough to protect RCU uses inside the exception. So
+         * just return immediately if we detect we are in an IRQ.
+         */
+        if (in_interrupt())
+                return;
+
+        WARN_ON_ONCE(!current->mm);
+
+        local_irq_save(flags);
+        if (__this_cpu_read(context_tracking.active) &&
+            __this_cpu_read(context_tracking.state) != IN_USER) {
+                __this_cpu_write(context_tracking.state, IN_USER);
+                rcu_user_enter();
+        }
+        local_irq_restore(flags);
+}
+
+void user_exit(void)
+{
+        unsigned long flags;
+
+        /*
+         * Some contexts may involve an exception occuring in an irq,
+         * leading to that nesting:
+         * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
+         * This would mess up the dyntick_nesting count though. And rcu_irq_*()
+         * helpers are enough to protect RCU uses inside the exception. So
+         * just return immediately if we detect we are in an IRQ.
+         */
+        if (in_interrupt())
+                return;
+
+        local_irq_save(flags);
+        if (__this_cpu_read(context_tracking.state) == IN_USER) {
+                __this_cpu_write(context_tracking.state, IN_KERNEL);
+                rcu_user_exit();
+        }
+        local_irq_restore(flags);
+}
+
+void context_tracking_task_switch(struct task_struct *prev,
+                             struct task_struct *next)
+{
+        if (__this_cpu_read(context_tracking.active)) {
+                clear_tsk_thread_flag(prev, TIF_NOHZ);
+                set_tsk_thread_flag(next, TIF_NOHZ);
+        }
+}