From: Prarit Bhargava <prarit@redhat.com>
Subject: [RHEL5 PATCH]: BZ 213455 Fix panic in CPU hotplug
Date: Fri, 3 Nov 2006 09:15:47 -0500
Bugzilla: 213455
Message-Id: <20061103141547.13414.75512.sendpatchset@prarit.boston.redhat.com>
Changelog: Fix panic in CPU hotplug on ia64


Backport straight into RHEL5.

Fixing the confliction between CPU hot-add and IPI.

Successfully tested by Kei on Fujitsu box.

Fixes BZ 213445.

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-2.6.18-1.2740.el5-kei/arch/ia64/kernel/smp.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff -puN arch/ia64/kernel/smp.c~bz213455-fix-panic-cpuhp arch/ia64/kernel/smp.c
--- linux-2.6.18-1.2740.el5/arch/ia64/kernel/smp.c~bz213455-fix-panic-cpuhp	2006-11-01 23:36:02.000000000 -0500
+++ linux-2.6.18-1.2740.el5-kei/arch/ia64/kernel/smp.c	2006-11-01 23:37:57.000000000 -0500
@@ -382,10 +382,14 @@ int
 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());
@@ -397,8 +401,6 @@ smp_call_function (void (*func) (void *i
 	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);

_