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[tip/core/rcu,1/7] rcu: Fix comment about _rcu_barrier()/orphanage exclusion

Message ID 1351616076-25617-1-git-send-email-paulmck@linux.vnet.ibm.com
State Accepted
Commit abfd6e58aed4f89fd69b9b17bc4b4527efe3a645
Headers show

Commit Message

Paul E. McKenney Oct. 30, 2012, 4:54 p.m. UTC 
From: "Paul E. McKenney" <paul.mckenney@linaro.org>

In the old days, _rcu_barrier() acquired ->onofflock to exclude
rcu_send_cbs_to_orphanage(), which allowed the latter to avoid memory
barriers in callback handling.  However, _rcu_barrier() recently started
doing get_online_cpus() to lock out CPU-hotplug operations entirely, which
means that the comment in rcu_send_cbs_to_orphanage() that talks about
->onofflock is now obsolete.  This commit therefore fixes the comment.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
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Patch

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 74df86b..ac8aed8 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1581,8 +1581,8 @@  rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
 {
 	/*
 	 * Orphan the callbacks.  First adjust the counts.  This is safe
-	 * because ->onofflock excludes _rcu_barrier()'s adoption of
-	 * the callbacks, thus no memory barrier is required.
+	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
+	 * cannot be running now.  Thus no memory barrier is required.
 	 */
 	if (rdp->nxtlist != NULL) {
 		rsp->qlen_lazy += rdp->qlen_lazy;