linux-kernel - [PATCH v3 4/8] percpu-rwsem: introduce percpu_down_read

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Date:	Fri, 14 Aug 2015 19:19:57 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Dave Chinner <david@...morbit.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jan Kara <jack@...e.cz>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 4/8] percpu-rwsem: introduce percpu_down_read_trylock()

Add percpu_down_read_trylock(), it will have the user soon.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 include/linux/percpu-rwsem.h  |    1 +
 kernel/locking/percpu-rwsem.c |   13 +++++++++++++
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 3e58226..3ebf982 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -17,6 +17,7 @@ struct percpu_rw_semaphore {
 };
 
 extern void percpu_down_read(struct percpu_rw_semaphore *);
+extern int  percpu_down_read_trylock(struct percpu_rw_semaphore *);
 extern void percpu_up_read(struct percpu_rw_semaphore *);
 
 extern void percpu_down_write(struct percpu_rw_semaphore *);
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 2c54c64..4bc2127 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -73,6 +73,19 @@ void percpu_down_read(struct percpu_rw_semaphore *brw)
 	__up_read(&brw->rw_sem);
 }
 
+int percpu_down_read_trylock(struct percpu_rw_semaphore *brw)
+{
+	if (unlikely(!update_fast_ctr(brw, +1))) {
+		if (!__down_read_trylock(&brw->rw_sem))
+			return 0;
+		atomic_inc(&brw->slow_read_ctr);
+		__up_read(&brw->rw_sem);
+	}
+
+	rwsem_acquire_read(&brw->rw_sem.dep_map, 0, 1, _RET_IP_);
+	return 1;
+}
+
 void percpu_up_read(struct percpu_rw_semaphore *brw)
 {
 	rwsem_release(&brw->rw_sem.dep_map, 1, _RET_IP_);
-- 
1.5.5.1

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