From: Davidlohr Bueso <dave@stgolabs.net>
Date: Mon, 18 Nov 2019 15:19:35 -0800
Subject: locking/percpu-rwsem: Fold __percpu_up_read()
Patch-mainline: v5.7-rc1
Git-commit: ac8dec420970f5cbaf2f6eda39153a60ec5b257b
References: bsc#1162702

Now that __percpu_up_read() is only ever used from percpu_up_read()
merge them, it's a small function.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20200131151540.212415454@infradead.org
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 include/linux/percpu-rwsem.h  | 19 +++++++++++++++----
 kernel/exit.c                 |  1 +
 kernel/locking/percpu-rwsem.c | 15 ---------------
 3 files changed, 16 insertions(+), 19 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index f5ecf6a8a1dd..5e033fe1ff4e 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -43,7 +43,6 @@ is_static struct percpu_rw_semaphore name = {				\
 	__DEFINE_PERCPU_RWSEM(name, static)
 
 extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
-extern void __percpu_up_read(struct percpu_rw_semaphore *);
 
 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
 {
@@ -103,10 +102,22 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 	/*
 	 * Same as in percpu_down_read().
 	 */
-	if (likely(rcu_sync_is_idle(&sem->rss)))
+	if (likely(rcu_sync_is_idle(&sem->rss))) {
 		__this_cpu_dec(*sem->read_count);
-	else
-		__percpu_up_read(sem); /* Unconditional memory barrier */
+	} else {
+		/*
+		 * slowpath; reader will only ever wake a single blocked
+		 * writer.
+		 */
+		smp_mb(); /* B matches C */
+		/*
+		 * In other words, if they see our decrement (presumably to
+		 * aggregate zero, as that is the only time it matters) they
+		 * will also see our critical section.
+		 */
+		__this_cpu_dec(*sem->read_count);
+		rcuwait_wake_up(&sem->writer);
+	}
 	preempt_enable();
 }
 
diff --git a/kernel/exit.c b/kernel/exit.c
index 2833ffb0c211..f64a8f9d412a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -258,6 +258,7 @@ void rcuwait_wake_up(struct rcuwait *w)
 		wake_up_process(task);
 	rcu_read_unlock();
 }
+EXPORT_SYMBOL_GPL(rcuwait_wake_up);
 
 /*
  * Determine if a process group is "orphaned", according to the POSIX
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index a136677543b4..8048a9a255d5 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -177,21 +177,6 @@ bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
 }
 EXPORT_SYMBOL_GPL(__percpu_down_read);
 
-void __percpu_up_read(struct percpu_rw_semaphore *sem)
-{
-	smp_mb(); /* B matches C */
-	/*
-	 * In other words, if they see our decrement (presumably to aggregate
-	 * zero, as that is the only time it matters) they will also see our
-	 * critical section.
-	 */
-	__this_cpu_dec(*sem->read_count);
-
-	/* Prod writer to re-evaluate readers_active_check() */
-	rcuwait_wake_up(&sem->writer);
-}
-EXPORT_SYMBOL_GPL(__percpu_up_read);
-
 #define per_cpu_sum(var)						\
 ({									\
 	typeof(var) __sum = 0;						\
-- 
2.16.4