[PATCH tip/core/rcu 0/12] Miscellaneous fixes for 3.15

[PATCH tip/core/rcu 0/12] Miscellaneous fixes for 3.15

[Paul E. McKenney]

Hello!

This series provides miscellaneous fixes;

1.	Add ACCESS_ONCE() to uses of ->n_force_qs_lh.

2.	Stop tracking FSF's postal address.

3.	Remove ACCESS_ONCE() from the volatile-declared jiffies.

4.	Glue ASCII strings together, courtesy of Joe Perches.

5.	Indentation and spacing fixes, courtesy of Joe Perches.

6.	Define rcu_assign_pointer() in terms of Peter Zijlstra's shiny
	new smp_store_release().

7.	Disambiguate CONFIG_RCU_NOCB_CPUs, courtesy of Paul Bolle.

8.	Move SRCU work to power-efficient workqueue, courtesy of
	Shaibal Dutta.

9-12.	Downgrade rcu_dereference_raw() to rcu_access_pointer() in
	cases where there is no subsequent dereferencing.

							Thanx, Paul

------------------------------------------------------------------------

 b/block/blk-cgroup.c       |    2 -
 b/block/blk-ioc.c          |    2 -
 b/fs/file.c                |    2 -
 b/include/linux/rculist.h  |   17 ++++-----
 b/include/linux/rcupdate.h |    4 +-
 b/include/linux/rcutiny.h  |    4 +-
 b/include/linux/rcutree.h  |    4 +-
 b/include/linux/srcu.h     |    4 +-
 b/kernel/ksysfs.c          |    2 +
 b/kernel/notifier.c        |    2 -
 b/kernel/rcu/rcu.h         |    4 +-
 b/kernel/rcu/srcu.c        |    4 +-
 b/kernel/rcu/tiny.c        |    4 +-
 b/kernel/rcu/tiny_plugin.h |    4 +-
 b/kernel/rcu/torture.c     |    4 +-
 b/kernel/rcu/tree.c        |    4 +-
 b/kernel/rcu/tree.h        |    4 +-
 b/kernel/rcu/tree_plugin.h |    4 +-
 b/kernel/rcu/tree_trace.c  |    2 -
 b/kernel/rcu/update.c      |    4 +-
 include/linux/rcupdate.h   |   82 ++++++++++++++++++++-------------------------
 kernel/rcu/rcu.h           |    2 -
 kernel/rcu/srcu.c          |    5 +-
 kernel/rcu/torture.c       |    4 +-
 kernel/rcu/tree.c          |   10 ++---
 kernel/rcu/tree_plugin.h   |    2 -
 kernel/rcu/tree_trace.c    |    4 +-
 27 files changed, 92 insertions(+), 98 deletions(-)

[PATCH tip/core/rcu 01/12] rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses

[Paul E. McKenney]

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

[PATCH tip/core/rcu 02/12] rcu: Stop tracking FSF's postal address

[Paul E. McKenney]

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

All of the RCU source files have the usual GPL header, which contains a
long-obsolete postal address for FSF.  To avoid the need to track the
FSF office's movements, this commit substitutes the URL where GPL may
be found.

Reported-by: Greg KH <gregkh@linuxfoundation.org>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 4 ++--
 include/linux/rcutiny.h  | 4 ++--
 include/linux/rcutree.h  | 4 ++--
 include/linux/srcu.h     | 4 ++--
 kernel/rcu/rcu.h         | 4 ++--
 kernel/rcu/srcu.c        | 4 ++--
 kernel/rcu/tiny.c        | 4 ++--
 kernel/rcu/tiny_plugin.h | 4 ++--
 kernel/rcu/torture.c     | 4 ++--
 kernel/rcu/tree.c        | 4 ++--
 kernel/rcu/tree.h        | 4 ++--
 kernel/rcu/tree_plugin.h | 4 ++--
 kernel/rcu/tree_trace.c  | 4 ++--
 kernel/rcu/update.c      | 4 ++--
 14 files changed, 28 insertions(+), 28 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 72bf3a01a4ee..b200756ea4c0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2001
  *
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 6f01771b571c..c364e9148de2 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2008
  *
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 72137ee8c603..08b084068967 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2008
  *
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 9b058eecd403..a2783cb5d275 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright (C) IBM Corporation, 2006
  * Copyright (C) Fujitsu, 2012
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 79c3877e9c5b..1bd787fddcb2 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2011
  *
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 3318d8284384..5db7e9272d37 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright (C) IBM Corporation, 2006
  * Copyright (C) Fujitsu, 2012
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 1254f312d024..53b95bbf4abb 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2008
  *
diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index 280d06cae352..431528520562 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -14,8 +14,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright (c) 2010 Linaro
  *
diff --git a/kernel/rcu/torture.c b/kernel/rcu/torture.c
index 732f8ae3086a..ab7dd192a50b 100644
--- a/kernel/rcu/torture.c
+++ b/kernel/rcu/torture.c
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright (C) IBM Corporation, 2005, 2006
  *
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e64157798624..321feef0f5c0 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2008
  *
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 8c19873f1ac9..75dc3c39a02a 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -13,8 +13,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2008
  *
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 6e2ef4b2b920..f9b9cdd36c8d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -14,8 +14,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright Red Hat, 2009
  * Copyright IBM Corporation, 2009
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index d1f1e64a6d72..5cdc62e1beeb 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2008
  *
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c54609faf233..fd0d5b5b8e7c 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -12,8 +12,8 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * Copyright IBM Corporation, 2001
  *
-- 
1.8.1.5

[PATCH tip/core/rcu 03/12] rcu: Remove ACCESS_ONCE() from jiffies

[Paul E. McKenney]

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

Because jiffies is one of a very few variables marked "volatile", there
is no need to use ACCESS_ONCE() when accessing it.  This commit therefore
removes the redundant ACCESS_ONCE() wrappers.

Reported by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/torture.c | 4 ++--
 kernel/rcu/tree.c    | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/torture.c b/kernel/rcu/torture.c
index ab7dd192a50b..022c5312b725 100644
--- a/kernel/rcu/torture.c
+++ b/kernel/rcu/torture.c
@@ -1352,7 +1352,7 @@ rcu_torture_shutdown(void *arg)
 	unsigned long jiffies_snap;
 
 	VERBOSE_PRINTK_STRING("rcu_torture_shutdown task started");
-	jiffies_snap = ACCESS_ONCE(jiffies);
+	jiffies_snap = jiffies;
 	while (ULONG_CMP_LT(jiffies_snap, shutdown_time) &&
 	       !kthread_should_stop()) {
 		delta = shutdown_time - jiffies_snap;
@@ -1361,7 +1361,7 @@ rcu_torture_shutdown(void *arg)
 				 "rcu_torture_shutdown task: %lu jiffies remaining\n",
 				 torture_type, delta);
 		schedule_timeout_interruptible(delta);
-		jiffies_snap = ACCESS_ONCE(jiffies);
+		jiffies_snap = jiffies;
 	}
 	if (kthread_should_stop()) {
 		VERBOSE_PRINTK_STRING("rcu_torture_shutdown task stopping");
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 321feef0f5c0..73c3cd2b87ac 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -837,7 +837,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * to the next.  Only do this for the primary flavor of RCU.
 	 */
 	if (rdp->rsp == rcu_state &&
-	    ULONG_CMP_GE(ACCESS_ONCE(jiffies), rdp->rsp->jiffies_resched)) {
+	    ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
 		rdp->rsp->jiffies_resched += 5;
 		resched_cpu(rdp->cpu);
 	}
@@ -847,7 +847,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 
 static void record_gp_stall_check_time(struct rcu_state *rsp)
 {
-	unsigned long j = ACCESS_ONCE(jiffies);
+	unsigned long j = jiffies;
 	unsigned long j1;
 
 	rsp->gp_start = j;
@@ -1005,7 +1005,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 
 	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
 		return;
-	j = ACCESS_ONCE(jiffies);
+	j = jiffies;
 
 	/*
 	 * Lots of memory barriers to reject false positives.
-- 
1.8.1.5

[PATCH tip/core/rcu 04/12] rcu: Glue ASCII strings together

[Paul E. McKenney]

From: Joe Perches <joe@perches.com>

Split strings make it difficult to find the code that resulted in a
given console message, so this commit glues split strings back together
despite the resulting long lines.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b200756ea4c0..d946d3660633 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -479,11 +479,9 @@ static inline void rcu_preempt_sleep_check(void)
 	do {								\
 		rcu_preempt_sleep_check();				\
 		rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),	\
-				   "Illegal context switch in RCU-bh"	\
-				   " read-side critical section");	\
+				   "Illegal context switch in RCU-bh read-side critical section"); \
 		rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),	\
-				   "Illegal context switch in RCU-sched"\
-				   " read-side critical section");	\
+				   "Illegal context switch in RCU-sched read-side critical section"); \
 	} while (0)
 
 #else /* #ifdef CONFIG_PROVE_RCU */
@@ -518,16 +516,14 @@ static inline void rcu_preempt_sleep_check(void)
 #define __rcu_dereference_check(p, c, space) \
 	({ \
 		typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
-		rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
-				      " usage"); \
+		rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
 		rcu_dereference_sparse(p, space); \
 		smp_read_barrier_depends(); \
 		((typeof(*p) __force __kernel *)(_________p1)); \
 	})
 #define __rcu_dereference_protected(p, c, space) \
 	({ \
-		rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
-				      " usage"); \
+		rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
 		rcu_dereference_sparse(p, space); \
 		((typeof(*p) __force __kernel *)(p)); \
 	})
@@ -542,8 +538,7 @@ static inline void rcu_preempt_sleep_check(void)
 	({ \
 		typeof(p) _________p1 = ACCESS_ONCE(p); \
 		rcu_lockdep_assert(c, \
-				   "suspicious rcu_dereference_index_check()" \
-				   " usage"); \
+				   "suspicious rcu_dereference_index_check() usage"); \
 		smp_read_barrier_depends(); \
 		(_________p1); \
 	})
-- 
1.8.1.5

[PATCH tip/core/rcu 05/12] rcu: Indentation and spacing fixes.

[Paul E. McKenney]

From: Joe Perches <joe@perches.com>

This commit outdents expression-statement macros, thus repairing a few
line-length complaints.  Also fix some spacing errors called out by
checkpatch.pl.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rculist.h  | 17 +++++++-------
 include/linux/rcupdate.h | 58 ++++++++++++++++++++++++------------------------
 2 files changed, 38 insertions(+), 37 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index dbaf99084112..8183b46fbaa2 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -247,9 +247,10 @@ static inline void list_splice_init_rcu(struct list_head *list,
  * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
  */
 #define list_entry_rcu(ptr, type, member) \
-	({typeof (*ptr) __rcu *__ptr = (typeof (*ptr) __rcu __force *)ptr; \
-	 container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
-	})
+({ \
+	typeof(*ptr) __rcu *__ptr = (typeof(*ptr) __rcu __force *)ptr; \
+	container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
+})
 
 /**
  * Where are list_empty_rcu() and list_first_entry_rcu()?
@@ -285,11 +286,11 @@ static inline void list_splice_init_rcu(struct list_head *list,
  * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
  */
 #define list_first_or_null_rcu(ptr, type, member) \
-	({struct list_head *__ptr = (ptr); \
-	  struct list_head *__next = ACCESS_ONCE(__ptr->next); \
-	  likely(__ptr != __next) ? \
-		list_entry_rcu(__next, type, member) : NULL; \
-	})
+({ \
+	struct list_head *__ptr = (ptr); \
+	struct list_head *__next = ACCESS_ONCE(__ptr->next); \
+	likely(__ptr != __next) ? list_entry_rcu(__next, type, member) : NULL; \
+})
 
 /**
  * list_for_each_entry_rcu	-	iterate over rcu list of given type
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d946d3660633..278a9da69ec4 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -508,40 +508,40 @@ static inline void rcu_preempt_sleep_check(void)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __rcu_access_pointer(p, space) \
-	({ \
-		typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
-		rcu_dereference_sparse(p, space); \
-		((typeof(*p) __force __kernel *)(_________p1)); \
-	})
+({ \
+	typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
+	rcu_dereference_sparse(p, space); \
+	((typeof(*p) __force __kernel *)(_________p1)); \
+})
 #define __rcu_dereference_check(p, c, space) \
-	({ \
-		typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
-		rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
-		rcu_dereference_sparse(p, space); \
-		smp_read_barrier_depends(); \
-		((typeof(*p) __force __kernel *)(_________p1)); \
-	})
+({ \
+	typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
+	rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
+	rcu_dereference_sparse(p, space); \
+	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+	((typeof(*p) __force __kernel *)(_________p1)); \
+})
 #define __rcu_dereference_protected(p, c, space) \
-	({ \
-		rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
-		rcu_dereference_sparse(p, space); \
-		((typeof(*p) __force __kernel *)(p)); \
-	})
+({ \
+	rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
+	rcu_dereference_sparse(p, space); \
+	((typeof(*p) __force __kernel *)(p)); \
+})
 
 #define __rcu_access_index(p, space) \
-	({ \
-		typeof(p) _________p1 = ACCESS_ONCE(p); \
-		rcu_dereference_sparse(p, space); \
-		(_________p1); \
-	})
+({ \
+	typeof(p) _________p1 = ACCESS_ONCE(p); \
+	rcu_dereference_sparse(p, space); \
+	(_________p1); \
+})
 #define __rcu_dereference_index_check(p, c) \
-	({ \
-		typeof(p) _________p1 = ACCESS_ONCE(p); \
-		rcu_lockdep_assert(c, \
-				   "suspicious rcu_dereference_index_check() usage"); \
-		smp_read_barrier_depends(); \
-		(_________p1); \
-	})
+({ \
+	typeof(p) _________p1 = ACCESS_ONCE(p); \
+	rcu_lockdep_assert(c, \
+			   "suspicious rcu_dereference_index_check() usage"); \
+	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+	(_________p1); \
+})
 
 /**
  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
-- 
1.8.1.5

[PATCH tip/core/rcu 06/12] rcu: Define rcu_assign_pointer() in terms of smp_store_release()

[Paul E. McKenney]

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

The new smp_store_release() function provides better guarantees than did
rcu_assign_pointer(), and potentially less overhead on some architectures.
The guarantee that smp_store_release() provides that rcu_assign_pointer()
does that is obscure, but its lack could cause considerable confusion.
This guarantee is illustrated by the following code fragment:

	struct foo {
		int a;
		int b;
		int c;
		struct foo *next;
	};
	struct foo foo1;
	struct foo foo2;
	struct foo __rcu *foop;

	...

	foo2.a = 1;
	foo2.b = 2;
	BUG_ON(foo2.c);
	rcu_assign_pointer(foop, &foo);

	...

	fp = rcu_dereference(foop);
	fp.c = 3;

The current rcu_assign_pointer() semantics permit the BUG_ON() to
trigger because rcu_assign_pointer()'s smp_wmb() is not guaranteed to
order prior reads against later writes.  This commit therefore upgrades
rcu_assign_pointer() from smp_wmb() to smp_store_release() to avoid this
counter-intuitive outcome.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 278a9da69ec4..32decf1a9c6c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -44,6 +44,7 @@
 #include <linux/debugobjects.h>
 #include <linux/bug.h>
 #include <linux/compiler.h>
+#include <asm/barrier.h>
 
 #ifdef CONFIG_RCU_TORTURE_TEST
 extern int rcutorture_runnable; /* for sysctl */
@@ -580,12 +581,7 @@ static inline void rcu_preempt_sleep_check(void)
  * please be careful when making changes to rcu_assign_pointer() and the
  * other macros that it invokes.
  */
-#define rcu_assign_pointer(p, v) \
-	do { \
-		smp_wmb(); \
-		ACCESS_ONCE(p) = RCU_INITIALIZER(v); \
-	} while (0)
-
+#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
 
 /**
  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
-- 
1.8.1.5

[PATCH tip/core/rcu 07/12] rcu: Disambiguate CONFIG_RCU_NOCB_CPUs

[Paul E. McKenney]

From: Paul Bolle <pebolle@tiscali.nl>

This commit fixes a grammar issue in the rcu_nohz_full_cpu() comment
header, so that it is clear that the plural is CPUs not Kconfig options.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index f9b9cdd36c8d..fffe4178a23d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2893,7 +2893,7 @@ static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
  * CPU unless the grace period has extended for too long.
  *
  * This code relies on the fact that all NO_HZ_FULL CPUs are also
- * CONFIG_RCU_NOCB_CPUs.
+ * CONFIG_RCU_NOCB_CPU CPUs.
  */
 static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
 {
-- 
1.8.1.5

[PATCH tip/core/rcu 08/12] rcu: Move SRCU grace period work to power efficient workqueue

[Paul E. McKenney]

From: Shaibal Dutta <shaibal.dutta@broadcom.com>

For better use of CPU idle time, allow the scheduler to select the CPU
on which the SRCU grace period work would be scheduled. This improves
idle residency time and conserves power.

This functionality is enabled when CONFIG_WQ_POWER_EFFICIENT is selected.

Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Shaibal Dutta <shaibal.dutta@broadcom.com>
[zoran.markovic@linaro.org: Rebased to latest kernel version. Added commit
message. Fixed code alignment.]
Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 5db7e9272d37..2359779e1daa 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -398,7 +398,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	rcu_batch_queue(&sp->batch_queue, head);
 	if (!sp->running) {
 		sp->running = true;
-		schedule_delayed_work(&sp->work, 0);
+		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
 }
@@ -674,7 +674,8 @@ static void srcu_reschedule(struct srcu_struct *sp)
 	}
 
 	if (pending)
-		schedule_delayed_work(&sp->work, SRCU_INTERVAL);
+		queue_delayed_work(system_power_efficient_wq,
+				   &sp->work, SRCU_INTERVAL);
 }
 
 /*
-- 
1.8.1.5

[PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Paul E. McKenney]

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 __alloc_fd(),
which simply compares the RCU-protected pointer against NULL with no
dereferencing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
---
 fs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/file.c b/fs/file.c
index db25c2bdfe46..18f7d27855c4 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -497,7 +497,7 @@ repeat:
 	error = fd;
 #if 1
 	/* Sanity check */
-	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
+	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
 		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
 		rcu_assign_pointer(fdt->fd[fd], NULL);
 	}
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Josh Triplett]

On Mon, Feb 17, 2014 at 01:35:56PM -0800, Paul E. McKenney wrote:
> 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 __alloc_fd(),
> which simply compares the RCU-protected pointer against NULL with no
> dereferencing.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: linux-fsdevel@vger.kernel.org

I'm beginning to wonder if this common pattern ought to have an
rcu_pointer_is_null(), which would not return the pointer, only the
boolean.

Regardless, for this patch:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  fs/file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index db25c2bdfe46..18f7d27855c4 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -497,7 +497,7 @@ repeat:
>  	error = fd;
>  #if 1
>  	/* Sanity check */
> -	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
> +	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
>  		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
>  		rcu_assign_pointer(fdt->fd[fd], NULL);
>  	}
> -- 
> 1.8.1.5
> 

Re: [PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Paul E. McKenney]

On Mon, Feb 17, 2014 at 02:00:15PM -0800, Josh Triplett wrote:
> On Mon, Feb 17, 2014 at 01:35:56PM -0800, Paul E. McKenney wrote:
> > 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 __alloc_fd(),
> > which simply compares the RCU-protected pointer against NULL with no
> > dereferencing.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: linux-fsdevel@vger.kernel.org
> 
> I'm beginning to wonder if this common pattern ought to have an
> rcu_pointer_is_null(), which would not return the pointer, only the
> boolean.

Or perhaps an rcu_compare_pointer() to also handle the various cases like:

	if (rcu_dereference_raw(foop) == barp) ...

I added the problem to the RCU cleanup list on the OPW site, and
your solution or my elaboration of it might be the right thing to do.
(Inspected all 1300 uses of members of the rcu_dereference() family of
functions last week, and was feeling a bit buggy-eyed at the end...)

							Thanx, Paul

> Regardless, for this patch:
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> 
> >  fs/file.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/file.c b/fs/file.c
> > index db25c2bdfe46..18f7d27855c4 100644
> > --- a/fs/file.c
> > +++ b/fs/file.c
> > @@ -497,7 +497,7 @@ repeat:
> >  	error = fd;
> >  #if 1
> >  	/* Sanity check */
> > -	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
> > +	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
> >  		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
> >  		rcu_assign_pointer(fdt->fd[fd], NULL);
> >  	}
> > -- 
> > 1.8.1.5
> > 
> 

Re: [PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Josh Triplett]

On Mon, Feb 17, 2014 at 03:05:11PM -0800, Paul E. McKenney wrote:
> On Mon, Feb 17, 2014 at 02:00:15PM -0800, Josh Triplett wrote:
> > On Mon, Feb 17, 2014 at 01:35:56PM -0800, Paul E. McKenney wrote:
> > > 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 __alloc_fd(),
> > > which simply compares the RCU-protected pointer against NULL with no
> > > dereferencing.
> > > 
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > > Cc: linux-fsdevel@vger.kernel.org
> > 
> > I'm beginning to wonder if this common pattern ought to have an
> > rcu_pointer_is_null(), which would not return the pointer, only the
> > boolean.
> 
> Or perhaps an rcu_compare_pointer() to also handle the various cases like:
> 
> 	if (rcu_dereference_raw(foop) == barp) ...
> 
> I added the problem to the RCU cleanup list on the OPW site, and
> your solution or my elaboration of it might be the right thing to do.
> (Inspected all 1300 uses of members of the rcu_dereference() family of
> functions last week, and was feeling a bit buggy-eyed at the end...)

rcu_pointer_eq and/or rcu_pointer_neq might make sense, yeah, as
self-documenting versions of the most sensible way to do the operation,
to steer people away from rcu_dereference or rcu_dereference_raw.

- Jsoh Triplett

> 							Thanx, Paul
> 
> > Regardless, for this patch:
> > Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> > 
> > >  fs/file.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/file.c b/fs/file.c
> > > index db25c2bdfe46..18f7d27855c4 100644
> > > --- a/fs/file.c
> > > +++ b/fs/file.c
> > > @@ -497,7 +497,7 @@ repeat:
> > >  	error = fd;
> > >  #if 1
> > >  	/* Sanity check */
> > > -	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
> > > +	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
> > >  		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
> > >  		rcu_assign_pointer(fdt->fd[fd], NULL);
> > >  	}
> > > -- 
> > > 1.8.1.5
> > > 
> > 
> 

Re: [PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Paul E. McKenney]

On Mon, Feb 17, 2014 at 04:04:31PM -0800, Josh Triplett wrote:
> On Mon, Feb 17, 2014 at 03:05:11PM -0800, Paul E. McKenney wrote:
> > On Mon, Feb 17, 2014 at 02:00:15PM -0800, Josh Triplett wrote:
> > > On Mon, Feb 17, 2014 at 01:35:56PM -0800, Paul E. McKenney wrote:
> > > > 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 __alloc_fd(),
> > > > which simply compares the RCU-protected pointer against NULL with no
> > > > dereferencing.
> > > > 
> > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > > > Cc: linux-fsdevel@vger.kernel.org
> > > 
> > > I'm beginning to wonder if this common pattern ought to have an
> > > rcu_pointer_is_null(), which would not return the pointer, only the
> > > boolean.
> > 
> > Or perhaps an rcu_compare_pointer() to also handle the various cases like:
> > 
> > 	if (rcu_dereference_raw(foop) == barp) ...
> > 
> > I added the problem to the RCU cleanup list on the OPW site, and
> > your solution or my elaboration of it might be the right thing to do.
> > (Inspected all 1300 uses of members of the rcu_dereference() family of
> > functions last week, and was feeling a bit buggy-eyed at the end...)
> 
> rcu_pointer_eq and/or rcu_pointer_neq might make sense, yeah, as
> self-documenting versions of the most sensible way to do the operation,
> to steer people away from rcu_dereference or rcu_dereference_raw.

Good point!  I added this to http://kernelnewbies.org/OPWIntro-RCU?action=show,
crediting you for the idea.

							Thanx, Paul

> - Jsoh Triplett
> 
> > 							Thanx, Paul
> > 
> > > Regardless, for this patch:
> > > Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> > > 
> > > >  fs/file.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/file.c b/fs/file.c
> > > > index db25c2bdfe46..18f7d27855c4 100644
> > > > --- a/fs/file.c
> > > > +++ b/fs/file.c
> > > > @@ -497,7 +497,7 @@ repeat:
> > > >  	error = fd;
> > > >  #if 1
> > > >  	/* Sanity check */
> > > > -	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
> > > > +	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
> > > >  		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
> > > >  		rcu_assign_pointer(fdt->fd[fd], NULL);
> > > >  	}
> > > > -- 
> > > > 1.8.1.5
> > > > 
> > > 
> > 
> 

[PATCH tip/core/rcu 10/12] block: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Paul E. McKenney]

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

Re: [PATCH tip/core/rcu 10/12] block: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Jens Axboe]

On Mon, Feb 17 2014, Paul E. McKenney wrote:
> 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.

Thanks Paul, applied.

-- 
Jens Axboe

[PATCH tip/core/rcu 11/12] notifier: Substitute rcu_access_pointer() for rcu_dereference_raw()

[Paul E. McKenney]

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
__blocking_notifier_call_chain() which simply compares the RCU-protected
pointer against NULL with no dereferencing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/notifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 2d5cc4ccff7f..db4c8b08a50c 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -309,7 +309,7 @@ int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 	 * racy then it does not matter what the result of the test
 	 * is, we re-check the list after having taken the lock anyway:
 	 */
-	if (rcu_dereference_raw(nh->head)) {
+	if (rcu_access_pointer(nh->head)) {
 		down_read(&nh->rwsem);
 		ret = notifier_call_chain(&nh->head, val, v, nr_to_call,
 					nr_calls);
-- 
1.8.1.5

[PATCH tip/core/rcu 12/12] rcu: Fix sparse warning for rcu_expedited from kernel/ksysfs.c

[Paul E. McKenney]

From: Paul Gortmaker <paul.gortmaker@windriver.com>

This commit fixes the follwoing warning:

kernel/ksysfs.c:143:5: warning: symbol 'rcu_expedited' was not declared. Should it be static?

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
[ paulmck: Moved the declaration to include/linux/rcupdate.h to avoid
	   including the RCU-internal rcu.h file outside of RCU. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 1 +
 kernel/ksysfs.c          | 2 ++
 kernel/rcu/rcu.h         | 2 --
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 32decf1a9c6c..f3706c6b2e21 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -46,6 +46,7 @@
 #include <linux/compiler.h>
 #include <asm/barrier.h>
 
+extern int rcu_expedited; /* for sysctl */
 #ifdef CONFIG_RCU_TORTURE_TEST
 extern int rcutorture_runnable; /* for sysctl */
 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index d945a949760f..e660964086e2 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -19,6 +19,8 @@
 #include <linux/sched.h>
 #include <linux/capability.h>
 
+#include <linux/rcupdate.h>	/* rcu_expedited */
+
 #define KERNEL_ATTR_RO(_name) \
 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
 
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 1bd787fddcb2..af2e60a8425d 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -116,8 +116,6 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 	}
 }
 
-extern int rcu_expedited;
-
 #ifdef CONFIG_RCU_STALL_COMMON
 
 extern int rcu_cpu_stall_suppress;
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 0/12] Miscellaneous fixes for 3.15

[Josh Triplett]

On Mon, Feb 17, 2014 at 01:35:33PM -0800, Paul E. McKenney wrote:
> Hello!
> 
> This series provides miscellaneous fixes;
> 
> 1.	Add ACCESS_ONCE() to uses of ->n_force_qs_lh.
> 
> 2.	Stop tracking FSF's postal address.
> 
> 3.	Remove ACCESS_ONCE() from the volatile-declared jiffies.
> 
> 4.	Glue ASCII strings together, courtesy of Joe Perches.
> 
> 5.	Indentation and spacing fixes, courtesy of Joe Perches.
> 
> 6.	Define rcu_assign_pointer() in terms of Peter Zijlstra's shiny
> 	new smp_store_release().
> 
> 7.	Disambiguate CONFIG_RCU_NOCB_CPUs, courtesy of Paul Bolle.
> 
> 8.	Move SRCU work to power-efficient workqueue, courtesy of
> 	Shaibal Dutta.
> 
> 9-12.	Downgrade rcu_dereference_raw() to rcu_access_pointer() in
> 	cases where there is no subsequent dereferencing.

For all 12:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
>  b/block/blk-cgroup.c       |    2 -
>  b/block/blk-ioc.c          |    2 -
>  b/fs/file.c                |    2 -
>  b/include/linux/rculist.h  |   17 ++++-----
>  b/include/linux/rcupdate.h |    4 +-
>  b/include/linux/rcutiny.h  |    4 +-
>  b/include/linux/rcutree.h  |    4 +-
>  b/include/linux/srcu.h     |    4 +-
>  b/kernel/ksysfs.c          |    2 +
>  b/kernel/notifier.c        |    2 -
>  b/kernel/rcu/rcu.h         |    4 +-
>  b/kernel/rcu/srcu.c        |    4 +-
>  b/kernel/rcu/tiny.c        |    4 +-
>  b/kernel/rcu/tiny_plugin.h |    4 +-
>  b/kernel/rcu/torture.c     |    4 +-
>  b/kernel/rcu/tree.c        |    4 +-
>  b/kernel/rcu/tree.h        |    4 +-
>  b/kernel/rcu/tree_plugin.h |    4 +-
>  b/kernel/rcu/tree_trace.c  |    2 -
>  b/kernel/rcu/update.c      |    4 +-
>  include/linux/rcupdate.h   |   82 ++++++++++++++++++++-------------------------
>  kernel/rcu/rcu.h           |    2 -
>  kernel/rcu/srcu.c          |    5 +-
>  kernel/rcu/torture.c       |    4 +-
>  kernel/rcu/tree.c          |   10 ++---
>  kernel/rcu/tree_plugin.h   |    2 -
>  kernel/rcu/tree_trace.c    |    4 +-
>  27 files changed, 92 insertions(+), 98 deletions(-)
>