Re: [PATCH v2] Locking: Let PREEMPT_RT compile again with new rwsem asserts.

From: Waiman Long
Date: Tue Mar 19 2024 - 20:58:37 EST


On 3/19/24 14:20, Sebastian Andrzej Siewior wrote:
The commit cited below broke the build for PREEMPT_RT because
rwsem_assert_held_write_nolockdep() passes a struct rw_semaphore but
rw_base_assert_held_write() expects struct rwbase_rt. Fixing the type
alone leads to the problem that WARN_ON() is not found because bug.h is
missing.

In order to resolve this:
- Keep the assert (WARN_ON()) in rwsem.h (not rwbase_rt.h)
- Make rwsem_assert_held_write_nolockdep() do the implementation
specific (rw_base) writer check.
- Replace the "inline" with __always_inline which was used before.

Fixes: f70405afc99b1 ("locking: Add rwsem_assert_held() and rwsem_assert_held_write()")
Reported-by: Clark Williams <williams@xxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
v1…v2:
- Merge rwsem_held_write() into rwsem_assert_held_write_nolockdep() as
per Waiman Long / Matthew Wilcox.

include/linux/rwbase_rt.h | 4 ++--
include/linux/rwsem.h | 6 +++---
2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/rwbase_rt.h b/include/linux/rwbase_rt.h
index 29c4e4f243e47..f2394a409c9d5 100644
--- a/include/linux/rwbase_rt.h
+++ b/include/linux/rwbase_rt.h
@@ -31,9 +31,9 @@ static __always_inline bool rw_base_is_locked(const struct rwbase_rt *rwb)
return atomic_read(&rwb->readers) != READER_BIAS;
}
-static inline void rw_base_assert_held_write(const struct rwbase_rt *rwb)
+static __always_inline bool rw_base_is_write_locked(const struct rwbase_rt *rwb)
{
- WARN_ON(atomic_read(&rwb->readers) != WRITER_BIAS);
+ return atomic_read(&rwb->readers) == WRITER_BIAS;
}
static __always_inline bool rw_base_is_contended(const struct rwbase_rt *rwb)
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 4f1c18992f768..c8b543d428b0a 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -167,14 +167,14 @@ static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
return rw_base_is_locked(&sem->rwbase);
}
-static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
+static __always_inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
{
WARN_ON(!rwsem_is_locked(sem));
}
-static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+static __always_inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
{
- rw_base_assert_held_write(sem);
+ WARN_ON(!rw_base_is_write_locked(&sem->rwbase));
}
static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>