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Subject[RFC][PATCH 06/13] percpu-rwsem: Provide percpu_down_read_trylock()

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/percpu-rwsem.h | 17 +++++++++++++++++
kernel/locking/percpu-rwsem.c | 12 ++++++++++++
2 files changed, 29 insertions(+)

--- 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 bool __percpu_down_read_trylock(struct percpu_rw_semaphore *);
extern void __percpu_up_read(struct percpu_rw_semaphore *);

static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
@@ -45,6 +46,22 @@ static inline void percpu_down_read(stru
*/
}

+static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
+{
+ bool ret = true;
+
+ preempt_disable();
+ __this_cpu_inc(*sem->refcount);
+ if (unlikely(!rcu_sync_is_idle(&sem->rss)))
+ ret = __percpu_down_read_trylock(sem);
+ preempt_enable();
+
+ if (ret)
+ rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
+
+ return ret;
+}
+
static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
{
/*
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -80,6 +80,18 @@ void __percpu_down_read(struct percpu_rw
preempt_disable();
}

+bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
+{
+ smp_mb(); /* A matches D */
+
+ if (likely(smp_load_acquire(&sem->state) != readers_block))
+ return true;
+
+ __percpu_up_read(sem);
+
+ return false;
+}
+
void __percpu_up_read(struct percpu_rw_semaphore *sem)
{
smp_mb(); /* B matches C */

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