kernel/cpu.c: create a CPU_STARTING cpu_chain notifier

Right now, there is no notifier that is called on a new cpu, before the new
cpu begins processing interrupts/softirqs.
Various kernel function would need that notification, e.g. kvm works around
by calling smp_call_function_single(), rcu polls cpu_online_map.

The patch adds a CPU_STARTING notification. It also adds a helper function
that sends the message to all cpu_chain handlers.

Tested on x86-64.
All other archs are untested. Especially on sparc, I'm not sure if I got
it right.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index da2698b0fdd1..b86fa2ffca0c 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -213,9 +213,16 @@ static inline int notifier_to_errno(int ret)
 #define CPU_DOWN_FAILED         0x0006 /* CPU (unsigned)v NOT going down */
 #define CPU_DEAD                0x0007 /* CPU (unsigned)v dead */
 #define CPU_DYING               0x0008 /* CPU (unsigned)v not running any task,
-                                        * not handling interrupts, soon dead */
+                                        * not handling interrupts, soon dead.
+                                        * Called on the dying cpu, interrupts
+                                        * are already disabled. Must not
+                                        * sleep, must not fail */
 #define CPU_POST_DEAD           0x0009 /* CPU (unsigned)v dead, cpu_hotplug
                                         * lock is dropped */
+#define CPU_STARTING            0x000A /* CPU (unsigned)v soon running.
+                                        * Called on the new cpu, just before
+                                        * enabling interrupts. Must not sleep,
+                                        * must not fail */
 
 /* Used for CPU hotplug events occuring while tasks are frozen due to a suspend
  * operation in progress
@@ -229,6 +236,7 @@ static inline int notifier_to_errno(int ret)
 #define CPU_DOWN_FAILED_FROZEN  (CPU_DOWN_FAILED | CPU_TASKS_FROZEN)
 #define CPU_DEAD_FROZEN         (CPU_DEAD | CPU_TASKS_FROZEN)
 #define CPU_DYING_FROZEN        (CPU_DYING | CPU_TASKS_FROZEN)
+#define CPU_STARTING_FROZEN     (CPU_STARTING | CPU_TASKS_FROZEN)
 
 /* Hibernation and suspend events */
 #define PM_HIBERNATION_PREPARE  0x0001 /* Going to hibernate */