linux-kernel - [PATCH] locking/rwsem: Introduce __rwsem_spin_on

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Message-Id: <20211015183255.3788750-1-yanfei.xu@windriver.com>
Date:   Sat, 16 Oct 2021 02:32:55 +0800
From:   Yanfei Xu <yanfei.xu@...driver.com>
To:     peterz@...radead.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, boqun.feng@...il.com
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] locking/rwsem: Introduce __rwsem_spin_on_owner()

'enum owner_state' is only declared when CONFIG_RWSEM_SPIN_ON_OWNER
is selected. To avoid the build failure, we introduce
__rwsem_spin_on_owner function.

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
---
 kernel/locking/rwsem.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 2bd914187399..7d85c85ad8a5 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -634,7 +634,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 }
 
 /*
- * The rwsem_spin_on_owner() function returns the following 4 values
+ * The __rwsem_spin_on_owner() function returns the following 4 values
  * depending on the lock owner state.
  *   OWNER_NULL  : owner is currently NULL
  *   OWNER_WRITER: when owner changes and is a writer
@@ -665,7 +665,7 @@ rwsem_owner_state(struct task_struct *owner, unsigned long flags)
 }
 
 static noinline enum owner_state
-rwsem_spin_on_owner(struct rw_semaphore *sem)
+__rwsem_spin_on_owner(struct rw_semaphore *sem)
 {
 	struct task_struct *new, *owner;
 	unsigned long flags, new_flags;
@@ -712,6 +712,17 @@ rwsem_spin_on_owner(struct rw_semaphore *sem)
 	return state;
 }
 
+static inline enum owner_state
+rwsem_spin_on_owner(struct rw_semaphore *sem)
+{
+	enum owner_state state;
+
+	preempt_disable();
+	state = __rwsem_spin_on_owner(sem);
+	preempt_enable();
+	return state;
+}
+
 /*
  * Calculate reader-owned rwsem spinning threshold for writer
  *
@@ -759,7 +770,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
 	for (;;) {
 		enum owner_state owner_state;
 
-		owner_state = rwsem_spin_on_owner(sem);
+		owner_state = __rwsem_spin_on_owner(sem);
 		if (!(owner_state & OWNER_SPINNABLE))
 			break;
 
@@ -831,7 +842,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
 		 * quit spinning.
 		 *
 		 * If the owner is a writer, the need_resched() check is
-		 * done inside rwsem_spin_on_owner(). If the owner is not
+		 * done inside __rwsem_spin_on_owner(). If the owner is not
 		 * a writer, need_resched() check needs to be done here.
 		 */
 		if (owner_state != OWNER_WRITER) {
@@ -1023,7 +1034,6 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
 	enum writer_wait_state wstate;
 	struct rwsem_waiter waiter;
 	struct rw_semaphore *ret = sem;
-	enum owner_state owner_state;
 	DEFINE_WAKE_Q(wake_q);
 
 	/* do optimistic spinning and steal lock if possible */
@@ -1099,12 +1109,9 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
 		 * In this case, we attempt to acquire the lock again
 		 * without sleeping.
 		 */
-		if (wstate == WRITER_HANDOFF) {
-			preempt_disable();
-			owner_state = rwsem_spin_on_owner(sem);
-			preempt_enable();
-			if (owner_state == OWNER_NULL)
-				goto trylock_again;
+		if (wstate == WRITER_HANDOFF &&
+		    rwsem_spin_on_owner(sem) == OWNER_NULL) {
+			goto trylock_again;
 		}
 
 		/* Block until there are no active lockers. */
-- 
2.27.0