linux-kernel - [PATCH v4 2/2] rcu: change rcu_dereference

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Date:	Mon, 30 Jun 2014 18:18:52 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/2] rcu: change rcu_dereference_check(c) to check "c"
	first

Change the order of "c" and "_held" checks in rcu_dereference_check(),
this can help if __builtin_constant_p(c).

CONFIG_DEBUG_LOCK_ALLOC + CONFIG_PROVE_RCU + CONFIG_TREE_RCU_TRACE

	- 5578795 3026776 14757888 23363459
	+ 5542443 3014040 14757888 23314371

saves 49088 bytes according to size vmlinux.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 include/linux/rcupdate.h |    6 +++---
 include/linux/srcu.h     |    2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b82d1d6..e8c55d8 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -694,7 +694,7 @@ static inline void rcu_preempt_sleep_check(void)
  * annotated as __rcu.
  */
 #define rcu_dereference_check(p, c) \
-	__rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
+	__rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
 
 /**
  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
@@ -704,7 +704,7 @@ static inline void rcu_preempt_sleep_check(void)
  * This is the RCU-bh counterpart to rcu_dereference_check().
  */
 #define rcu_dereference_bh_check(p, c) \
-	__rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
+	__rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
 
 /**
  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
@@ -714,7 +714,7 @@ static inline void rcu_preempt_sleep_check(void)
  * This is the RCU-sched counterpart to rcu_dereference_check().
  */
 #define rcu_dereference_sched_check(p, c) \
-	__rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
+	__rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
 				__rcu)
 
 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 5c06289..eae58d4 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -184,7 +184,7 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
  * lockdep_is_held() calls.
  */
 #define srcu_dereference_check(p, sp, c) \
-	__rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
+	__rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
 
 /**
  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
-- 
1.5.5.1

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