patches/locking-percpu-rwsem-use-swait-for-the-wating-writer.patch

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 21 Nov 2016 19:26:15 +0100
Subject: [PATCH] locking/percpu-rwsem: use swait for the wating writer

Use struct swait_queue_head instead of wait_queue_head_t for the waiting
writer. The swait implementation is smaller and lightweight compared to
wait_queue_head_t.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/percpu-rwsem.h  |    6 +++---
 kernel/locking/percpu-rwsem.c |    6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -4,7 +4,7 @@
 #include <linux/atomic.h>
 #include <linux/rwsem.h>
 #include <linux/percpu.h>
-#include <linux/wait.h>
+#include <linux/swait.h>
 #include <linux/rcu_sync.h>
 #include <linux/lockdep.h>
 
@@ -12,7 +12,7 @@ struct percpu_rw_semaphore {
 	struct rcu_sync		rss;
 	unsigned int __percpu	*read_count;
 	struct rw_semaphore	rw_sem;
-	wait_queue_head_t	writer;
+	struct swait_queue_head	writer;
 	int			readers_block;
 };
 
@@ -22,7 +22,7 @@ static struct percpu_rw_semaphore name =
 	.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC),	\
 	.read_count = &__percpu_rwsem_rc_##name,			\
 	.rw_sem = __RWSEM_INITIALIZER(name.rw_sem),			\
-	.writer = __WAIT_QUEUE_HEAD_INITIALIZER(name.writer),		\
+	.writer = __SWAIT_QUEUE_HEAD_INITIALIZER(name.writer),		\
 }
 
 extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -18,7 +18,7 @@ int __percpu_init_rwsem(struct percpu_rw
 	/* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
 	rcu_sync_init(&sem->rss, RCU_SCHED_SYNC);
 	__init_rwsem(&sem->rw_sem, name, rwsem_key);
-	init_waitqueue_head(&sem->writer);
+	init_swait_queue_head(&sem->writer);
 	sem->readers_block = 0;
 	return 0;
 }
@@ -103,7 +103,7 @@ void __percpu_up_read(struct percpu_rw_s
 	__this_cpu_dec(*sem->read_count);
 
 	/* Prod writer to recheck readers_active */
-	wake_up(&sem->writer);
+	swake_up(&sem->writer);
 }
 EXPORT_SYMBOL_GPL(__percpu_up_read);
 
@@ -160,7 +160,7 @@ void percpu_down_write(struct percpu_rw_
 	 */
 
 	/* Wait for all now active readers to complete. */
-	wait_event(sem->writer, readers_active_check(sem));
+	swait_event(sem->writer, readers_active_check(sem));
 }
 EXPORT_SYMBOL_GPL(percpu_down_write);