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Date:   Mon, 29 Jul 2019 17:24:28 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andrea Parri <andrea.parri@amarulasolutions.com>
Cc:     Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        Jan Stancek <jstancek@redhat.com>,
        Waiman Long <longman@redhat.com>, dbueso@suse.de,
        mingo@redhat.com, jade.alglave@arm.com, paulmck@linux.vnet.ibm.com
Subject: Re: [PATCH 1/4] locking/rwsem: Add missing ACQUIRE to read_slowpath
 exit when queue is empty
Message-ID: <20190729152428.GH31398@hirez.programming.kicks-ass.net>
References: <20190718134954.496297975@infradead.org>
 <20190718135205.916241783@infradead.org>
 <20190719084956.GA6750@andrea>
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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.