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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>,
	Jens Axboe <axboe@kernel.dk>
Subject: [PATCH tip/core/rcu 10/12] block: Substitute rcu_access_pointer() for rcu_dereference_raw()
Date: Mon, 17 Feb 2014 13:35:57 -0800	[thread overview]
Message-ID: <1392672959-6386-10-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1392672959-6386-1-git-send-email-paulmck@linux.vnet.ibm.com>

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

(Trivial patch.)

If the code is looking at the RCU-protected pointer itself, but not
dereferencing it, the rcu_dereference() functions can be downgraded to
rcu_access_pointer().  This commit makes this downgrade in blkg_destroy()
and ioc_destroy_icq(), both of which simply compare the RCU-protected
pointer against another pointer with no dereferencing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Jens Axboe <axboe@kernel.dk>
---
 block/blk-cgroup.c | 2 +-
 block/blk-ioc.c    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 4e491d9b5292..b6e95b5e262f 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -336,7 +336,7 @@ static void blkg_destroy(struct blkcg_gq *blkg)
 	 * under queue_lock.  If it's not pointing to @blkg now, it never
 	 * will.  Hint assignment itself can race safely.
 	 */
-	if (rcu_dereference_raw(blkcg->blkg_hint) == blkg)
+	if (rcu_access_pointer(blkcg->blkg_hint) == blkg)
 		rcu_assign_pointer(blkcg->blkg_hint, NULL);
 
 	/*
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 242df01413f6..1a27f45ec776 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -68,7 +68,7 @@ static void ioc_destroy_icq(struct io_cq *icq)
 	 * under queue_lock.  If it's not pointing to @icq now, it never
 	 * will.  Hint assignment itself can race safely.
 	 */
-	if (rcu_dereference_raw(ioc->icq_hint) == icq)
+	if (rcu_access_pointer(ioc->icq_hint) == icq)
 		rcu_assign_pointer(ioc->icq_hint, NULL);
 
 	ioc_exit_icq(icq);
-- 
1.8.1.5


  parent reply	other threads:[~2014-02-17 21:38 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 ` [PATCH tip/core/rcu 01/12] rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses Paul E. McKenney
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   ` Paul E. McKenney [this message]
2014-02-18 20:21     ` [PATCH tip/core/rcu 10/12] block: " 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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