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Date: Wed, 6 Jun 2018 12:26:13 +0200
From: Christoph Hellwig <hch@lst.de>
To: David Sterba <dsterba@suse.cz>
Cc: Andreas Gruenbacher <agruenba@redhat.com>,
        cluster-devel@redhat.com, Christoph Hellwig <hch@lst.de>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v8 03/10] iomap: Complete partial direct I/O writes
        synchronously
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References: <20180604193123.27655-1-agruenba@redhat.com> <20180604193123.27655-4-agruenba@redhat.com> <20180605121024.t6indzioavvfonxk@twin.jikos.cz>
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On Tue, Jun 05, 2018 at 02:10:24PM +0200, David Sterba wrote:
> On Mon, Jun 04, 2018 at 09:31:16PM +0200, Andreas Gruenbacher wrote:
> > @@ -1062,8 +1063,9 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> >  	if (ret < 0)
> >  		iomap_dio_set_error(dio, ret);
> >  
> > +	smp_mb__before_atomic();
> >  	if (!atomic_dec_and_test(&dio->ref)) {
> 
> The barrier should be documented. I tried to do a quick look around the
> code if it's clear why it's there but it's not. Thanks.

It doesn't really make sense.  smp_mb__before_atomic is for relaxed
atomic operations, which atomic_dec_and_test is not.