linux-kernel - [PATCH RFC 1/3] locking/rwsem: make owner helpers globally available

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Message-ID: <20250612042005.99602-2-lance.yang@linux.dev>
Date: Thu, 12 Jun 2025 12:19:24 +0800
From: Lance Yang <ioworker0@...il.com>
To: akpm@...ux-foundation.org
Cc: zi.li@...ux.dev,
	anna.schumaker@...cle.com,
	boqun.feng@...il.com,
	joel.granados@...nel.org,
	jstultz@...gle.com,
	kent.overstreet@...ux.dev,
	leonylgao@...cent.com,
	linux-kernel@...r.kernel.org,
	longman@...hat.com,
	mhiramat@...nel.org,
	mingo@...hat.com,
	mingzhe.yang@...com,
	peterz@...radead.org,
	rostedt@...dmis.org,
	senozhatsky@...omium.org,
	tfiga@...omium.org,
	will@...nel.org,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH RFC 1/3] locking/rwsem: make owner helpers globally available

From: Lance Yang <lance.yang@...ux.dev>

In preparation for extending blocker tracking to support rwsems, make the
rwsem_owner() and is_rwsem_reader_owned() helpers globally available for
determining if the blocker is a writer or one of the readers.

Signed-off-by: Lance Yang <lance.yang@...ux.dev>
---
 include/linux/rwsem.h  | 12 ++++++++++++
 kernel/locking/rwsem.c |  8 +++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index c8b543d428b0..544853bed5b9 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -132,6 +132,18 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
 	return !list_empty(&sem->wait_list);
 }
 
+#if defined(CONFIG_DEBUG_RWSEMS) || defined(CONFIG_DETECT_HUNG_TASK_BLOCKER)
+/*
+ * Return just the real task structure pointer of the owner
+ */
+extern struct task_struct *rwsem_owner(struct rw_semaphore *sem);
+
+/*
+ * Return true if the rwsem is owned by a reader.
+ */
+extern bool is_rwsem_reader_owned(struct rw_semaphore *sem);
+#endif
+
 #else /* !CONFIG_PREEMPT_RT */
 
 #include <linux/rwbase_rt.h>
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 2ddb827e3bea..6cb29442d4fc 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -181,11 +181,11 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
 	__rwsem_set_reader_owned(sem, current);
 }
 
-#ifdef CONFIG_DEBUG_RWSEMS
+#if defined(CONFIG_DEBUG_RWSEMS) || defined(CONFIG_DETECT_HUNG_TASK_BLOCKER)
 /*
  * Return just the real task structure pointer of the owner
  */
-static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
+struct task_struct *rwsem_owner(struct rw_semaphore *sem)
 {
 	return (struct task_struct *)
 		(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
@@ -194,7 +194,7 @@ static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
 /*
  * Return true if the rwsem is owned by a reader.
  */
-static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
+bool is_rwsem_reader_owned(struct rw_semaphore *sem)
 {
 	/*
 	 * Check the count to see if it is write-locked.
@@ -205,7 +205,9 @@ static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
 		return false;
 	return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
 }
+#endif
 
+#ifdef CONFIG_DEBUG_RWSEMS
 /*
  * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
  * is a task pointer in owner of a reader-owned rwsem, it will be the
-- 
2.49.0