[PATCH] Fix hibernate/resume in presence of PREEMPT_RCU and hotplug

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Hello!

This fixes a oops encountered when doing hibernate/resume in presence
of PREEMPT_RCU.  The problem was that the code failed to disable preemption
when accessing a per-CPU variable.  This is OK when called from code
that already has preemption disabled, but such is not the case from
the suspend/resume code path.

Reported-by: Dave Young <hidave.darkstar@gmail.com>
Tested-by: Dave Young <hidave.darkstar@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

 rcupreempt.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff -urpNa -X dontdiff linux-2.6.25-rc3/kernel/rcupreempt.c linux-2.6.25-rc3-rcuoffline/kernel/rcupreempt.c
--- linux-2.6.25-rc3/kernel/rcupreempt.c	2008-02-26 16:58:43.000000000 -0800
+++ linux-2.6.25-rc3-rcuoffline/kernel/rcupreempt.c	2008-02-26 17:04:17.000000000 -0800
@@ -702,8 +702,9 @@ void rcu_offline_cpu(int cpu)
 	 * fix.
 	 */
 
+	local_irq_save(flags);
 	rdp = RCU_DATA_ME();
-	spin_lock_irqsave(&rdp->lock, flags);
+	spin_lock(&rdp->lock);
 	*rdp->nexttail = list;
 	if (list)
 		rdp->nexttail = tail;