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Date: Wed, 11 May 2016 11:04:42 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        "David S. Miller" <davem@davemloft.net>,
        Tony Luck <tony.luck@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>, Waiman Long <Waiman.Long@hpe.com>
Subject: Re: [PATCH 03/11] locking, rwsem: introduce basis for
 down_write_killable
Message-ID: <20160511090442.GH16677@dhcp22.suse.cz>
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On Wed 11-05-16 10:44:01, Peter Zijlstra wrote:
[...]
> @@ -504,6 +502,18 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
>  	raw_spin_unlock_irq(&sem->wait_lock);
>  
>  	return ret;
> +
> +out_nolock:
> +	__set_current_state(TASK_RUNNING);
> +	raw_spin_lock_irq(&sem->wait_lock);
> +	list_del(&waiter.list);
> +	if (list_empty(&sem->wait_list))
> +		rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem);
> +	else
> +		__rwsem_do_wake(sem, RWSEM_WAKE_READERS);
> +	raw_spin_unlock_irq(&sem->wait_lock);
> +
> +	return ERR_PTR(-EINTR);
>  }

Looks much better but don't we have to check the count for potentially
pending writers?

-- 
Michal Hocko
SUSE Labs