linux-kernel - [PATCH RESEND 1/3] locking: add rwsem_is_write

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Message-ID: <8e343ccb9319433364f5949a69519f1bb521fc8a.1768569863.git.lorenzo.stoakes@oracle.com>
Date: Fri, 16 Jan 2026 13:36:45 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>, Jann Horn <jannh@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-rt-devel@...ts.linux.dev, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Clark Williams <clrkwllms@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH RESEND 1/3] locking: add rwsem_is_write_locked(), update non-lockdep asserts

As part of adding some additional lock asserts in mm, we wish to be able to
determine if a read/write semaphore is write-locked, so add
rwsem_is_write_locked() to do the write-lock equivalent of
rwsem_is_locked().

While we're here, update rwsem_assert_[write_]held_nolockdep() to utilise
the rwsem_is_[write_]locked() helpers directly to reduce code duplication,
and also update rwsem_is_locked() to take a const rwsem and return a
boolean.

This patch also updates the CONFIG_PREEMPT_RT helpers to do the same thing
there.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 include/linux/rwsem.h | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index f1aaf676a874..b25b7944ad99 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -70,19 +70,24 @@ struct rw_semaphore {
 #define RWSEM_WRITER_LOCKED		(1UL << 0)
 #define __RWSEM_COUNT_INIT(name)	.count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)

-static inline int rwsem_is_locked(struct rw_semaphore *sem)
+static inline bool rwsem_is_locked(const struct rw_semaphore *sem)
 {
 	return atomic_long_read(&sem->count) != RWSEM_UNLOCKED_VALUE;
 }

+static inline bool rwsem_is_write_locked(const struct rw_semaphore *sem)
+{
+	return atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED;
+}
+
 static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
 {
-	WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
+	WARN_ON(!rwsem_is_locked(sem));
 }

 static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
 {
-	WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED));
+	WARN_ON(!rwsem_is_write_locked(sem));
 }

 /* Common initializer macros and functions */
@@ -174,11 +179,16 @@ do {								\
 	__init_rwsem((sem), #sem, &__key);			\
 } while (0)

-static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
+static __always_inline bool rwsem_is_locked(const struct rw_semaphore *sem)
 {
 	return rw_base_is_locked(&sem->rwbase);
 }

+static __always_inline bool rwsem_is_write_locked(const struct rw_semaphore *sem)
+{
+	return rw_base_is_write_locked(&sem->rwbase);
+}
+
 static __always_inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
 {
 	WARN_ON(!rwsem_is_locked(sem));
@@ -186,7 +196,7 @@ static __always_inline void rwsem_assert_held_nolockdep(const struct rw_semaphor

 static __always_inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
 {
-	WARN_ON(!rw_base_is_write_locked(&sem->rwbase));
+	WARN_ON(!rwsem_is_write_locked(sem));
 }

 static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
--
2.52.0