3 files changed, 49 insertions, 0 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index 9943202b4355..864ff75d65f2 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -99,6 +99,7 @@ obj-$(CONFIG_SLOW_WORK) += slow-work.o
 obj-$(CONFIG_SLOW_WORK_DEBUG) += slow-work-debugfs.o
 obj-$(CONFIG_PERF_EVENTS) += perf_event.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
+obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
 
 ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
diff --git a/kernel/fork.c b/kernel/fork.c
index 3d6f121bbe8a..edeff9ceaab9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -64,6 +64,7 @@
 #include <linux/magic.h>
 #include <linux/perf_event.h>
 #include <linux/posix-timers.h>
+#include <linux/user-return-notifier.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -249,6 +250,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
                 goto out;
 
         setup_thread_stack(tsk, orig);
+        clear_user_return_notifier(tsk);
         stackend = end_of_stack(tsk);
         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 
diff --git a/kernel/user-return-notifier.c b/kernel/user-return-notifier.c
new file mode 100644
index 000000000000..03e2d6fd9b18
--- /dev/null
+++ b/kernel/user-return-notifier.c
@@ -0,0 +1,46 @@
+
+#include <linux/user-return-notifier.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+
+static DEFINE_PER_CPU(struct hlist_head, return_notifier_list);
+
+#define URN_LIST_HEAD per_cpu(return_notifier_list, raw_smp_processor_id())
+
+/*
+ * Request a notification when the current cpu returns to userspace.  Must be
+ * called in atomic context.  The notifier will also be called in atomic
+ * context.
+ */
+void user_return_notifier_register(struct user_return_notifier *urn)
+{
+        set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
+        hlist_add_head(&urn->link, &URN_LIST_HEAD);
+}
+EXPORT_SYMBOL_GPL(user_return_notifier_register);
+
+/*
+ * Removes a registered user return notifier.  Must be called from atomic
+ * context, and from the same cpu registration occured in.
+ */
+void user_return_notifier_unregister(struct user_return_notifier *urn)
+{
+        hlist_del(&urn->link);
+        if (hlist_empty(&URN_LIST_HEAD))
+                clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
+}
+EXPORT_SYMBOL_GPL(user_return_notifier_unregister);
+
+/* Calls registered user return notifiers */
+void fire_user_return_notifiers(void)
+{
+        struct user_return_notifier *urn;
+        struct hlist_node *tmp1, *tmp2;
+        struct hlist_head *head;
+
+        head = &get_cpu_var(return_notifier_list);
+        hlist_for_each_entry_safe(urn, tmp1, tmp2, head, link)
+                urn->on_user_return(urn);
+        put_cpu_var(return_notifier_list);
+}