x86-smp-remove-call-to-ipi_call_lock-ipi_call_unlock

ipi_call_lock/unlock() lock resp. unlock call_function.lock. This lock
protects only the call_function data structure itself, but it's
completely unrelated to cpu_online_mask. The mask to which the IPIs
are sent is calculated before call_function.lock is taken in
smp_call_function_many(), so the locking around set_cpu_online() is
pointless and can be removed.

[ tglx: Massaged changelog ]

Signed-off-by: Yong Zhang <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Acked-by: Srivatsa S. Bhat <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>

arch/x86/kernel/smpboot.c

@@ -255,22 +255,13 @@ notrace static void __cpuinit start_secondary(void *unused)
 	check_tsc_sync_target();
 
 	/*
-	 * We need to hold call_lock, so there is no inconsistency
-	 * between the time smp_call_function() determines number of
-	 * IPI recipients, and the time when the determination is made
-	 * for which cpus receive the IPI. Holding this
-	 * lock helps us to not include this cpu in a currently in progress
-	 * smp_call_function().
-	 *
 	 * We need to hold vector_lock so there the set of online cpus
 	 * does not change while we are assigning vectors to cpus.  Holding
 	 * this lock ensures we don't half assign or remove an irq from a cpu.
 	 */
-	ipi_call_lock();
 	lock_vector_lock();
 	set_cpu_online(smp_processor_id(), true);
 	unlock_vector_lock();
-	ipi_call_unlock();
 	per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
 	x86_platform.nmi_init();
 

arch/x86/xen/smp.c

@@ -80,9 +80,7 @@ static void __cpuinit cpu_bringup(void)
 
 	notify_cpu_starting(cpu);
 
-	ipi_call_lock();
 	set_cpu_online(cpu, true);
-	ipi_call_unlock();
 
 	this_cpu_write(cpu_state, CPU_ONLINE);