From 5197fcd09ab6dcc4df79edec7e8e27575276374c Mon Sep 17 00:00:00 2001
From: Yanfei Xu <yanfei.xu@windriver.com>
Date: Wed, 13 Oct 2021 21:41:54 +0800
Subject: [PATCH] locking/rwsem: Fix comments about reader optimistic lock stealing conditions
Git-commit: 5197fcd09ab6dcc4df79edec7e8e27575276374c
Patch-mainline: v5.16-rc1
References: bsc#1190137

After the commit 617f3ef95177 ("locking/rwsem: Remove reader
optimistic spinning"), reader doesn't support optimistic spinning
anymore, there is no need meet the condition which OSQ is empty.

BTW, add an unlikely() for the max reader wakeup check in the loop.

Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211013134154.1085649-4-yanfei.xu@windriver.com
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

---
 kernel/locking/rwsem.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 884aa08e0624..c51387a43265 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -56,7 +56,6 @@
  *
  * A fast path reader optimistic lock stealing is supported when the rwsem
  * is previously owned by a writer and the following conditions are met:
- *  - OSQ is empty
  *  - rwsem is not currently writer owned
  *  - the handoff isn't set.
  */
@@ -485,7 +484,7 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
 		/*
 		 * Limit # of readers that can be woken up per wakeup call.
 		 */
-		if (woken >= MAX_READERS_WAKEUP)
+		if (unlikely(woken >= MAX_READERS_WAKEUP))
 			break;
 	}
 
-- 
2.26.2