linux-kernel - Re: [PATCH 2/2] locking/rwbase_rt: Lockless reader waking up a writer

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Message-ID: <87ilz4fyzi.ffs@tglx>
Date:   Mon, 13 Sep 2021 14:20:49 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     peterz@...radead.org, mingo@...nel.org, rostedt@...dmis.org,
        longman@...hat.com, bigeasy@...utronix.de, boqun.feng@...il.com,
        dave@...olabs.net, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 2/2] locking/rwbase_rt: Lockless reader waking up a writer

On Wed, Sep 01 2021 at 15:28, Davidlohr Bueso wrote:
> diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
> index 4ba15088e640..3444bc709973 100644
> --- a/kernel/locking/rwbase_rt.c
> +++ b/kernel/locking/rwbase_rt.c
> @@ -141,6 +141,7 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
>  {
>  	struct rt_mutex_base *rtm = &rwb->rtmutex;
>  	struct task_struct *owner;
> +	DEFINE_WAKE_Q(wake_q);
>  
>  	raw_spin_lock_irq(&rtm->wait_lock);
>  	/*
> @@ -151,9 +152,10 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
>  	 */
>  	owner = rt_mutex_owner(rtm);
>  	if (owner)
> -		wake_up_state(owner, state);
> +		wake_q_add(&wake_q, owner);

That's broken for rw_locks. See commit 456cfbc65cd072f4f53936ee5a37eb1447a7d3ba.

Thanks,

        tglx