linux-kernel - Re: [PATCH 1/4] locking/rwsem: Add missing ACQUIRE to read

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Message-ID: <20190729152428.GH31398@hirez.programming.kicks-ass.net>
Date:   Mon, 29 Jul 2019 17:24:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Jan Stancek <jstancek@...hat.com>,
        Waiman Long <longman@...hat.com>, dbueso@...e.de,
        mingo@...hat.com, jade.alglave@....com, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/4] locking/rwsem: Add missing ACQUIRE to read_slowpath
 exit when queue is empty

On Fri, Jul 19, 2019 at 10:49:56AM +0200, Andrea Parri wrote:
> > @@ -1032,6 +1032,8 @@ rwsem_down_read_slowpath(struct rw_semap
> >  		 */
> >  		if (adjustment && !(atomic_long_read(&sem->count) &
> >  		     (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
> > +			/* Provide lock ACQUIRE */
> > +			smp_acquire__after_ctrl_dep();
> 
> Does this also make the lock RCtso?  Or maybe RCtso was already
> guaranteed (and I'm failing to see why)?

I didn't specifically look for that, but I suspect not, esp given the
next patch.