linux-kernel - [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem

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Message-Id: <1526326267-22501-3-git-send-email-longman@redhat.com>
Date:   Mon, 14 May 2018 15:31:07 -0400
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Oleg Nesterov <oleg@...hat.com>,
        Amir Goldstein <amir73il@...il.com>, Jan Kara <jack@...e.cz>,
        Waiman Long <longman@...hat.com>
Subject: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

The percpu_rwsem_release() is called when the ownership of the embedded
rwsem is to be transferred to another task. The new owner, however, may
take a while to get the ownership of the lock via percpu_rwsem_acquire().
During that period, the rwsem is now marked as writer-owned with no
optimistic spinning.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 include/linux/percpu-rwsem.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index b1f37a8..dd37102 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -131,16 +131,16 @@ static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 					bool read, unsigned long ip)
 {
 	lock_release(&sem->rw_sem.dep_map, 1, ip);
-#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 	if (!read)
-		sem->rw_sem.owner = NULL;
-#endif
+		rwsem_set_writer_owned_nospin(&sem->rw_sem);
 }
 
 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
 					bool read, unsigned long ip)
 {
 	lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
+	if (!read)
+		rwsem_set_writer_owned(&sem->rw_sem, current);
 }
 
 #endif
-- 
1.8.3.1