Re: [patch V5 34/72] locking/rwlock: Provide RT variant

[Xiaoming Ni]

On 2021/8/16 5:28, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> Similar to rw_semaphores on RT the rwlock substitution is not writer fair
> because it's not feasible to have a writer inherit it's priority to
> multiple readers. Readers blocked on a writer follow the normal rules of
> priority inheritance. Like RT spinlocks RT rwlocks are state preserving
> across the slow lock operations (contended case).
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> V5: Add missing might_sleep() and fix lockdep init (Sebastian)
> ---
>   include/linux/rwlock_rt.h       |  140 ++++++++++++++++++++++++++++++++++++++++
>   include/linux/rwlock_types.h    |   49 ++++++++++----
>   include/linux/spinlock_rt.h     |    2
>   kernel/Kconfig.locks            |    2
>   kernel/locking/spinlock.c       |    7 ++
>   kernel/locking/spinlock_debug.c |    5 +
>   kernel/locking/spinlock_rt.c    |  131 +++++++++++++++++++++++++++++++++++++
>   7 files changed, 323 insertions(+), 13 deletions(-)
>   create mode 100644 include/linux/rwlock_rt.h
> ---
.....
> +
> +int __sched rt_rwlock_is_contended(rwlock_t *rwlock)
> +{
> +	return rw_base_is_contended(&rwlock->rwbase);
> +}
> +EXPORT_SYMBOL(rt_rwlock_is_contended);
> +

rt_rwlock_is_conted() exported but not declared in the header file?
Is this a special design or a mistake?

Thanks
Xiaoming Ni