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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
	peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com,
	edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com,
	oleg@redhat.com, sbw@mit.edu,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/12] rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses
Date: Mon, 17 Feb 2014 13:35:48 -0800	[thread overview]
Message-ID: <1392672959-6386-1-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20140217213533.GA5387@linux.vnet.ibm.com>

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The ->n_force_qs_lh field is accessed without the benefit of any
synchronization, so this commit adds the needed ACCESS_ONCE() wrappers.
Yes, increments to ->n_force_qs_lh can be lost, but contention should
be low and the field is strictly statistical in nature, so this is not
a problem.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c       | 4 ++--
 kernel/rcu/tree_trace.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b3d116cd072d..e64157798624 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2304,7 +2304,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
 		if (rnp_old != NULL)
 			raw_spin_unlock(&rnp_old->fqslock);
 		if (ret) {
-			rsp->n_force_qs_lh++;
+			ACCESS_ONCE(rsp->n_force_qs_lh)++;
 			return;
 		}
 		rnp_old = rnp;
@@ -2316,7 +2316,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
 	smp_mb__after_unlock_lock();
 	raw_spin_unlock(&rnp_old->fqslock);
 	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
-		rsp->n_force_qs_lh++;
+		ACCESS_ONCE(rsp->n_force_qs_lh)++;
 		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
 		return;  /* Someone beat us to it. */
 	}
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 4def475336d4..d1f1e64a6d72 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -273,7 +273,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 	seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
 		   rsp->n_force_qs, rsp->n_force_qs_ngp,
 		   rsp->n_force_qs - rsp->n_force_qs_ngp,
-		   rsp->n_force_qs_lh, rsp->qlen_lazy, rsp->qlen);
+		   ACCESS_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
 	for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
 		if (rnp->level != level) {
 			seq_puts(m, "\n");
-- 
1.8.1.5


  reply	other threads:[~2014-02-17 21:36 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-17 21:35 [PATCH tip/core/rcu 0/12] Miscellaneous fixes for 3.15 Paul E. McKenney
2014-02-17 21:35 ` Paul E. McKenney [this message]
2014-02-17 21:35   ` [PATCH tip/core/rcu 02/12] rcu: Stop tracking FSF's postal address Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 03/12] rcu: Remove ACCESS_ONCE() from jiffies Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 04/12] rcu: Glue ASCII strings together Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 05/12] rcu: Indentation and spacing fixes Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 06/12] rcu: Define rcu_assign_pointer() in terms of smp_store_release() Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 07/12] rcu: Disambiguate CONFIG_RCU_NOCB_CPUs Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 08/12] rcu: Move SRCU grace period work to power efficient workqueue Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw() Paul E. McKenney
2014-02-17 22:00     ` Josh Triplett
2014-02-17 23:05       ` Paul E. McKenney
2014-02-18  0:04         ` Josh Triplett
2014-02-18  0:27           ` Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 10/12] block: " Paul E. McKenney
2014-02-18 20:21     ` Jens Axboe
2014-02-17 21:35   ` [PATCH tip/core/rcu 11/12] notifier: " Paul E. McKenney
2014-02-17 21:35   ` [PATCH tip/core/rcu 12/12] rcu: Fix sparse warning for rcu_expedited from kernel/ksysfs.c Paul E. McKenney
2014-02-17 22:01 ` [PATCH tip/core/rcu 0/12] Miscellaneous fixes for 3.15 Josh Triplett

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