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Groups > linux.kernel > #1215679

[PATCH RFC tip/core/rcu 8/9] locking/percpu-rwsem: Clean up the lockdep annotations in percpu_down_read()

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From: Oleg Nesterov <oleg@redhat.com>

Based on Peter Zijlstra's earlier patch.

Change percpu_down_read() to use __down_read(), this way we can
do rwsem_acquire_read() unconditionally at the start to make this
code more symmetric and clean.

Originally-From: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/locking/percpu-rwsem.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 25b73448929c..61b678d784ce 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -69,14 +69,14 @@ static bool update_fast_ctr(struct percpu_rw_semaphore *brw, unsigned int val)
 void percpu_down_read(struct percpu_rw_semaphore *brw)
 {
 	might_sleep();
-	if (likely(update_fast_ctr(brw, +1))) {
-		rwsem_acquire_read(&brw->rw_sem.dep_map, 0, 0, _RET_IP_);
+	rwsem_acquire_read(&brw->rw_sem.dep_map, 0, 0, _RET_IP_);
+
+	if (likely(update_fast_ctr(brw, +1)))
 		return;
-	}
 
-	down_read(&brw->rw_sem);
+	/* Avoid rwsem_acquire_read() and rwsem_release() */
+	__down_read(&brw->rw_sem);
 	atomic_inc(&brw->slow_read_ctr);
-	/* avoid up_read()->rwsem_release() */
 	__up_read(&brw->rw_sem);
 }
 
-- 
1.8.1.5

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[PATCH RFC tip/core/rcu 1/9] rcu: Create rcu_sync infrastructure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 6/9] locking/percpu-rwsem: Make use of the rcu_sync infrastructure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 2/9] rcu_sync: Simplify rcu_sync using new rcu_sync_ops structure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 5/9] locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 7/9] locking/percpu-rwsem: Fix the comments outdated by rcu_sync "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 8/9] locking/percpu-rwsem: Clean up the lockdep annotations in percpu_down_read() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 3/9] rcu_sync: Add CONFIG_PROVE_RCU checks "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200

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