linux-kernel - Re: [PATCH] vhost/scsi: drop unnecessary smp_mb__after

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Message-ID: <CAJSP0QX_daRKAoXY2_w4Bmxv-fo5Kw1DgvYz7AUwJxGdEdw9Xg@mail.gmail.com>
Date:   Thu, 18 Apr 2019 09:56:17 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>, kvm <kvm@...r.kernel.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH] vhost/scsi: drop unnecessary smp_mb__after_atomic()

On Wed, Apr 17, 2019 at 6:57 AM Jason Wang <jasowang@...hat.com> wrote:
> On 2019/4/16 下午6:47, Stefan Hajnoczi wrote:
> > The vhost_scsi.ko code used several atomic variables at one point.
> > Later they were dropped or converted to regular ints protected by a
> > mutex.
> >
> > The commit that made these changes left an unused smp_mb__after_atomic()
> > in vhost_scsi_set_endpoint().  It was previously used after incrementing
> > vhost_scsi->vhost_ref_cnt but this field has been dropped:
> >
> >    -     atomic_inc(&vs->vhost_ref_cnt);
> >          smp_mb__after_atomic_inc();
> >
> > Reported-by: Andrea Parri <andrea.parri@...rulasolutions.com>
> > Fixes: 101998f6fcd680 ("tcm_vhost: Post-merge review changes requested by MST")
> > Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
> > ---
> >   drivers/vhost/scsi.c | 1 -
> >   1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> > index 618fb6461017..c090d177bd75 100644
> > --- a/drivers/vhost/scsi.c
> > +++ b/drivers/vhost/scsi.c
> > @@ -1443,7 +1443,6 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
> >                       tpg->tv_tpg_vhost_count++;
> >                       tpg->vhost_scsi = vs;
> >                       vs_tpg[tpg->tport_tpgt] = tpg;
> > -                     smp_mb__after_atomic();
> >                       match = true;
> >               }
> >               mutex_unlock(&tpg->tv_tpg_mutex);
>
>
> Looks like Paolo has sent an identical patch before this one.

Yes, Paolo's patch is fine.

Stefan