From c9e71002aacc9821e99531dcc130db88bbc8ad05 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Thu, 28 Feb 2008 11:51:07 -0800
Subject: rcupreempt: remove never-migrates assumption from
 rcu_process_callbacks()

This patch fixes a potentially invalid access to a per-CPU variable in
rcu_process_callbacks().

This per-CPU access needs to be done in such a way as to guarantee that
the code using it cannot move to some other CPU before all uses of the
value accessed have completed.  Even though this code is currently only
invoked from softirq context, which currrently cannot migrate to some
other CPU, life would be better if this code did not silently make such
an assumption.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/rcupreempt.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

(limited to 'kernel')

diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index 845abcd472b0..e9517014b57c 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -952,9 +952,11 @@ static void rcu_process_callbacks(struct softirq_action *unused)
 {
 	unsigned long flags;
 	struct rcu_head *next, *list;
-	struct rcu_data *rdp = RCU_DATA_ME();
+	struct rcu_data *rdp;
 
-	spin_lock_irqsave(&rdp->lock, flags);
+	local_irq_save(flags);
+	rdp = RCU_DATA_ME();
+	spin_lock(&rdp->lock);
 	list = rdp->donelist;
 	if (list == NULL) {
 		spin_unlock_irqrestore(&rdp->lock, flags);
-- 
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