linux-kernel - [PATCH v2 8/8] percpu-rwsem: cleanup the lockdep annotations in percpu_down

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Date:	Fri, 21 Aug 2015 19:43:03 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 8/8] percpu-rwsem: cleanup the lockdep annotations in
	percpu_down_read()

Stolen from Peter's 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.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/locking/percpu-rwsem.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 69704eb..5694849 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);
 }
 
-- 
1.5.5.1

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