[BUGFIX] [PATCH 1/2] cpu-hotplug: Fixing confliction between CPU hot-add and IPI

[Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>]

From: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>

---
Fixing the confliction between CPU hot-add and IPI.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Acked-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Index: linux-2.6.19-rc3/arch/ia64/kernel/smp.c
===================================================================
--- linux-2.6.19-rc3.orig/arch/ia64/kernel/smp.c	2006-10-27 18:40:47.000000000 +0900
+++ linux-2.6.19-rc3/arch/ia64/kernel/smp.c	2006-10-27 18:49:48.000000000 +0900
@@ -328,10 +328,14 @@
 smp_call_function (void (*func) (void *info), void *info, int nonatomic, int wait)
 {
 	struct call_data_struct data;
-	int cpus = num_online_cpus()-1;
+	int cpus;
 
-	if (!cpus)
+	spin_lock(&call_lock);
+	cpus = num_online_cpus() - 1;
+	if (!cpus) {
+		spin_unlock(&call_lock);
 		return 0;
+	}
 
 	/* Can deadlock when called with interrupts disabled */
 	WARN_ON(irqs_disabled());
@@ -343,8 +347,6 @@
 	if (wait)
 		atomic_set(&data.finished, 0);
 
-	spin_lock(&call_lock);
-
 	call_data = &data;
 	mb();	/* ensure store to call_data precedes setting of IPI_CALL_FUNC */
 	send_IPI_allbutself(IPI_CALL_FUNC);
-
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