[PATCH 02/27] smpboot: Add provisions for arch-specific locking around cpu_online_mask

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

We want to make smp booting as generic as possible and remove code
duplication in arch/ directories.

While manipulating the cpu_online_mask, x86 uses an additional lock, i.e.,
'vector_lock'. So provide a generic way to implement such arch-specific
extra locking, by providing weakly defined functions arch_vector_lock()
and arch_vector_unlock() which can be overriden by different architectures
suitably.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 kernel/smpboot.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 6c26133..5ae1805 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -107,6 +107,13 @@ void __weak __cpu_pre_online(void *arg) {}
 void __weak __cpu_post_online(void *arg) {}
 #endif
 
+/*
+ * Optional arch-specific locking for manipulating cpu_online_mask while
+ * bringing up secondary CPUs.
+ */
+void __weak arch_vector_lock(void) {}
+void __weak arch_vector_unlock(void) {}
+
 
 /**
  * smpboot_start_secondary - Generic way to boot secondary processors
@@ -129,8 +136,10 @@ void __cpuinit smpboot_start_secondary(void *arg)
 
 	__cpu_pre_online(arg);
 
-	/* Set the CPU in the cpu_online_mask */
+	/* Set the CPU in the cpu_online_mask with required locks held */
+	arch_vector_lock();
 	set_cpu_online(cpu, true);
+	arch_vector_unlock();
 
 	__cpu_post_online(arg);