On Thu, Jan 11, 2024 at 09:24:22PM +0000, Matthew Wilcox (Oracle) wrote:
> Modelled after lockdep_assert_held() and lockdep_assert_held_write(),
> but are always active, even when lockdep is disabled. Of course, they
> don't test that _this_ thread is the owner, but it's sufficient to catch
> many bugs and doesn't incur the same performance penalty as lockdep.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Looks good to me, having read this patchset backwards.
Acked-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> include/linux/rwbase_rt.h | 9 ++++++--
> include/linux/rwsem.h | 46 ++++++++++++++++++++++++++++++++++-----
> 2 files changed, 48 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/rwbase_rt.h b/include/linux/rwbase_rt.h
> index 1d264dd08625..29c4e4f243e4 100644
> --- a/include/linux/rwbase_rt.h
> +++ b/include/linux/rwbase_rt.h
> @@ -26,12 +26,17 @@ struct rwbase_rt {
> } while (0)
>
>
> -static __always_inline bool rw_base_is_locked(struct rwbase_rt *rwb)
> +static __always_inline bool rw_base_is_locked(const struct rwbase_rt *rwb)
> {
> return atomic_read(&rwb->readers) != READER_BIAS;
> }
>
> -static __always_inline bool rw_base_is_contended(struct rwbase_rt *rwb)
> +static inline void rw_base_assert_held_write(const struct rwbase_rt *rwb)
> +{
> + WARN_ON(atomic_read(&rwb->readers) != WRITER_BIAS);
> +}
> +
> +static __always_inline bool rw_base_is_contended(const struct rwbase_rt *rwb)
> {
> return atomic_read(&rwb->readers) > 0;
> }
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index 9c29689ff505..4f1c18992f76 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -66,14 +66,24 @@ struct rw_semaphore {
> #endif
> };
>
> -/* In all implementations count != 0 means locked */
> +#define RWSEM_UNLOCKED_VALUE 0UL
> +#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)
> {
> - return atomic_long_read(&sem->count) != 0;
> + return atomic_long_read(&sem->count) != RWSEM_UNLOCKED_VALUE;
> }
>
> -#define RWSEM_UNLOCKED_VALUE 0L
> -#define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
> +static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
> +{
> + WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
> +}
> +
> +static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
> +{
> + WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED));
> +}
>
> /* Common initializer macros and functions */
>
> @@ -152,11 +162,21 @@ do { \
> __init_rwsem((sem), #sem, &__key); \
> } while (0)
>
> -static __always_inline int rwsem_is_locked(struct rw_semaphore *sem)
> +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)
> +{
> + WARN_ON(!rwsem_is_locked(sem));
> +}
> +
> +static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
> +{
> + rw_base_assert_held_write(sem);
> +}
> +
> static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
> {
> return rw_base_is_contended(&sem->rwbase);
> @@ -169,6 +189,22 @@ static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
> * the RT specific variant.
> */
>
> +static inline void rwsem_assert_held(const struct rw_semaphore *sem)
> +{
> + if (IS_ENABLED(CONFIG_LOCKDEP))
> + lockdep_assert_held(sem);
> + else
> + rwsem_assert_held_nolockdep(sem);
> +}
> +
> +static inline void rwsem_assert_held_write(const struct rw_semaphore *sem)
> +{
> + if (IS_ENABLED(CONFIG_LOCKDEP))
> + lockdep_assert_held_write(sem);
> + else
> + rwsem_assert_held_write_nolockdep(sem);
> +}
> +
> /*
> * lock for reading
> */
> --
> 2.43.0
>
>
