[PATCH] Run softirqs on proper processor on offline

We take down ksoftirqds at CPU_DEAD time, so there is a brief period whereupon
there is a ksoftirqd thread for an offline processor, it is at this point that
->cpus_allowed won't have it pinned anymore.  An online processor would then
take down that ksoftirqd and exit it.

Ensure that we only offline the processor when it's safe and never run
softirqs in another processor's ksoftirqd context.  This also gets rid of the
warnings in ksoftirqd on cpu offline.
Signed-off-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/softirq.c

@@ -355,8 +355,12 @@ static int ksoftirqd(void * __bind_cpu)
 	set_current_state(TASK_INTERRUPTIBLE);
 
 	while (!kthread_should_stop()) {
-		if (!local_softirq_pending())
+		preempt_disable();
+		if (!local_softirq_pending()) {
+			preempt_enable_no_resched();
 			schedule();
+			preempt_disable();
+		}
 
 		__set_current_state(TASK_RUNNING);
 
@@ -364,14 +368,14 @@ static int ksoftirqd(void * __bind_cpu)
 			/* Preempt disable stops cpu going offline.
 			   If already offline, we'll be on wrong CPU:
 			   don't process */
-			preempt_disable();
 			if (cpu_is_offline((long)__bind_cpu))
 				goto wait_to_die;
 			do_softirq();
-			preempt_enable();
+			preempt_enable_no_resched();
 			cond_resched();
+			preempt_disable();
 		}
-
+		preempt_enable();
 		set_current_state(TASK_INTERRUPTIBLE);
 	}
 	__set_current_state(TASK_RUNNING);