linux-kernel - [PATCH] locking/rwsem: Make rwsem_is

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Date:   Tue,  7 Mar 2017 11:03:48 -0500
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: [PATCH] locking/rwsem: Make rwsem_is_contended() track status of OSQ

It was found that the current rwsem_is_contended() function did not
look at the status of the OSQ and hence would miss waiters on OSQ. So
that function is now modified to look at the OSQ as well.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 include/linux/rwsem.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index dd1d142..9cb64e3 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -71,8 +71,18 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
 
 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
+
+static inline bool rwsem_osq_is_locked(struct rw_semaphore *sem)
+{
+	return osq_is_locked(&sem->osq);
+}
 #else
 #define __RWSEM_OPT_INIT(lockname)
+
+static inline bool rwsem_osq_is_locked(struct rw_semaphore *sem)
+{
+	return false;
+}
 #endif
 
 #define __RWSEM_INITIALIZER(name)				\
@@ -103,7 +113,7 @@ extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  */
 static inline int rwsem_is_contended(struct rw_semaphore *sem)
 {
-	return !list_empty(&sem->wait_list);
+	return !list_empty(&sem->wait_list) || rwsem_osq_is_locked(sem);
 }
 
 /*
-- 
1.8.3.1