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

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Date:   Sat, 11 Sep 2021 10:59:11 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>,
        Mike Galbraith <efault@....de>
Subject: Re: [patch V5 34/72] locking/rwlock: Provide RT variant

On 2021/8/16 5:28, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> 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@...utronix.de>
> ---
> 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