[PATCH 2/3] percpu-rwsem: don't use percpu_rw_semaphore->rw_sem to exclude writers

2015-06-28 Thread Oleg Nesterov 
percpu_down_write() does down_write() to exclude both the readers and
other writers. We can rely on rcu_sync_enter() in exclusive mode and
take ->rw_sem right before wait_event().

Signed-off-by: Oleg Nesterov 
---
 kernel/locking/percpu-rwsem.c |3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 014d2f4..609c13b 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -139,8 +139,6 @@ static bool readers_active_check(struct percpu_rw_semaphore 
*sem)
 
 void percpu_down_write(struct percpu_rw_semaphore *sem)
 {
-   down_write(>rw_sem);
-
/* Notify readers to take the slow path. */
rcu_sync_enter(>rss);
 
@@ -158,6 +156,7 @@ void percpu_down_write(struct percpu_rw_semaphore *sem)
 * therefore will wait for them.
 */
 
+   down_write(>rw_sem);
/* Wait for all now active readers to complete. */
wait_event(sem->writer, readers_active_check(sem));
 }
-- 
1.5.5.1

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[PATCH 2/3] percpu-rwsem: don't use percpu_rw_semaphore-rw_sem to exclude writers

2015-06-28 Thread Oleg Nesterov 
percpu_down_write() does down_write() to exclude both the readers and
other writers. We can rely on rcu_sync_enter() in exclusive mode and
take -rw_sem right before wait_event().

Signed-off-by: Oleg Nesterov o...@redhat.com
---
 kernel/locking/percpu-rwsem.c |3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 014d2f4..609c13b 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -139,8 +139,6 @@ static bool readers_active_check(struct percpu_rw_semaphore 
*sem)
 
 void percpu_down_write(struct percpu_rw_semaphore *sem)
 {
-   down_write(sem-rw_sem);
-
/* Notify readers to take the slow path. */
rcu_sync_enter(sem-rss);
 
@@ -158,6 +156,7 @@ void percpu_down_write(struct percpu_rw_semaphore *sem)
 * therefore will wait for them.
 */
 
+   down_write(sem-rw_sem);
/* Wait for all now active readers to complete. */
wait_event(sem-writer, readers_active_check(sem));
 }
-- 
1.5.5.1

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