linux-kernel - Re: [PATCH v2] locking/rwsem: add acquire barrier to read

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Date:   Thu, 18 Jul 2019 07:36:52 -0400 (EDT)
From:   Jan Stancek <jstancek@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
        linux-kernel@...r.kernel.org, dbueso@...e.de, mingo@...hat.com,
        jade alglave <jade.alglave@....com>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v2] locking/rwsem: add acquire barrier to read_slowpath
 exit when queue is empty


----- 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.