linux-kernel - [PATCH 1/2] locking: Wire up rwlock_is_contended() on PREEMPT

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Date:   Mon,  6 Sep 2021 16:30:03 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH 1/2] locking: Wire up rwlock_is_contended() on PREEMPT_RT

rwlock_is_contended() should return 0 if there are no waiters pending
on that lock on, != 0 otherwise.
PREEMPT_RT's implementation of RW-locks provides
rt_rwlock_is_contended() which returns != 0 if there is a writer about
to acquire the lock. The only downside is that a writter, that is
using that function, will always see that this lock is contended even if
there are no readers or writters pending.

Wire up rwlock_is_contended() with RT's rt_rwlock_is_contended().

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/linux/rwlock_rt.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
index 49c1f3842ed5b..e482671ff49ee 100644
--- a/include/linux/rwlock_rt.h
+++ b/include/linux/rwlock_rt.h
@@ -30,6 +30,7 @@ extern void rt_read_unlock(rwlock_t *rwlock);
 extern void rt_write_lock(rwlock_t *rwlock);
 extern int rt_write_trylock(rwlock_t *rwlock);
 extern void rt_write_unlock(rwlock_t *rwlock);
+extern int rt_rwlock_is_contended(rwlock_t *rwlock);
 
 static __always_inline void read_lock(rwlock_t *rwlock)
 {
@@ -135,6 +136,6 @@ static __always_inline void write_unlock_irqrestore(rwlock_t *rwlock,
 	rt_write_unlock(rwlock);
 }
 
-#define rwlock_is_contended(lock)		(((void)(lock), 0))
+#define rwlock_is_contended(lock)		rt_rwlock_is_contended(lock)
 
 #endif /* __LINUX_RWLOCK_RT_H */
-- 
2.33.0