Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 18 Jul 2019 07:36:52 -0400 (EDT)
From:   Jan Stancek <jstancek@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
        linux-kernel@vger.kernel.org, dbueso@suse.de, mingo@redhat.com,
        jade alglave <jade.alglave@arm.com>, paulmck@linux.vnet.ibm.com
Message-ID: <466627724.868829.1563449812023.JavaMail.zimbra@redhat.com>
In-Reply-To: <20190718110928.GT3463@hirez.programming.kicks-ass.net>
References: <20190716185807.GJ3402@hirez.programming.kicks-ass.net> <20190717131335.b2ry43t2ov7ba4t4@willie-the-truck> <21ff5905-198b-6ea5-6c2a-9fb10cb48ea7@redhat.com> <20190717192200.GA17687@dustball.usersys.redhat.com> <20190718092640.52oliw3sid7gxyh6@willie-the-truck> <79224323.853324.1563447052432.JavaMail.zimbra@redhat.com> <20190718110446.GC3419@hirez.programming.kicks-ass.net> <20190718110928.GT3463@hirez.programming.kicks-ass.net>
Subject: Re: [PATCH v2] locking/rwsem: add acquire barrier to read_slowpath
 exit when queue is empty
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Thread-Topic: locking/rwsem: add acquire barrier to read_slowpath exit when queue is empty
Thread-Index: 2FC8jkf3xWoTPr5a8SlywdIbna06hA==
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


----- Original Message -----
> 
> It's simpler like so:
> 
> On Thu, Jul 18, 2019 at 01:04:46PM +0200, Peter Zijlstra wrote:
> > X = 0;
> > 
> > 	rwsem_down_read()
> > 	  for (;;) {
> > 	    set_current_state(TASK_UNINTERRUPTIBLE);
> >
> >								X = 1;
> >                                                               rwsem_up_write();
> > 								  rwsem_mark_wake()
> > 								    atomic_long_add(adjustment, &sem->count);
> > 								    smp_store_release(&waiter->task, NULL);
> > 
> > 	    if (!waiter.task)
> > 	      break;
> > 
> > 	    ...
> > 	  }
> > 
> > 	r = X;
> > 

I see - it looks possible. Thank you for this example.