linux-kernel - Re: [patch-rt] locking, rwlock-rt: do not save state multiple times in __write_rt

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Message-ID: <20170818090626.5u5tm3hakhhntx5y@linutronix.de>
Date:   Fri, 18 Aug 2017 11:06:27 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <efault@....de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch-rt] locking, rwlock-rt: do not save state multiple times
 in __write_rt_lock()

On 2017-08-09 14:04:48 [+0200], Mike Galbraith wrote:
> 
> Save state prior to entering the acquisition loop, otherwise we may
> initially see readers, but upon releasing ->wait_lock see none, loop
> back around, and having not slept, save TASK_UNINTERRUPTIBLE.
> 
> Signed-off-by_ Mike Galbraith <efault@....de>

applied but

> ---
>  kernel/locking/rwlock-rt.c |   37 ++++++++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 17 deletions(-)
> 
> --- a/kernel/locking/rwlock-rt.c
> +++ b/kernel/locking/rwlock-rt.c
> @@ -190,30 +190,33 @@ void __sched __write_rt_lock(struct rt_r
…
>  
> +	for (;;) {
>  		/* Have all readers left the critical region? */
> -		if (!atomic_read(&lock->readers)) {
> -			atomic_set(&lock->readers, WRITER_BIAS);
> -			raw_spin_lock(&self->pi_lock);
> -			__set_current_state_no_track(self->saved_state);
> -			self->saved_state = TASK_RUNNING;
> -			raw_spin_unlock(&self->pi_lock);
> -			raw_spin_unlock_irqrestore(&m->wait_lock, flags);
> -			return;

I kept this part where it is so the diff is smaller.

> -		}
> +		if (!atomic_read(&lock->readers))
> +			break;
>  }
>  
>  int __write_rt_trylock(struct rt_rw_lock *lock)

Sebastian