linux-kernel - Re: [PATCH 4/5] ceph: fix improper use of smp_mb__before

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Date:   Tue, 30 Apr 2019 17:08:43 +0800
From:   "Yan, Zheng" <ukernel@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrea Parri <andrea.parri@...rulasolutions.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, "Yan, Zheng" <zyan@...hat.com>,
        Sage Weil <sage@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
        ceph-devel <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH 4/5] ceph: fix improper use of smp_mb__before_atomic()

On Tue, Apr 30, 2019 at 4:26 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Apr 29, 2019 at 10:15:00PM +0200, Andrea Parri wrote:
> > This barrier only applies to the read-modify-write operations; in
> > particular, it does not apply to the atomic64_set() primitive.
> >
> > Replace the barrier with an smp_mb().
> >
>
> > @@ -541,7 +541,7 @@ static inline void __ceph_dir_set_complete(struct ceph_inode_info *ci,
> >                                          long long release_count,
> >                                          long long ordered_count)
> >  {
> > -     smp_mb__before_atomic();
>
> same
>         /*
>          * XXX: the comment that explain this barrier goes here.
>          */
>

makes sure operations that setup readdir cache (update page cache and
i_size) are strongly ordered with following atomic64_set.

> > +     smp_mb();
>
> >       atomic64_set(&ci->i_complete_seq[0], release_count);
> >       atomic64_set(&ci->i_complete_seq[1], ordered_count);
> >  }
> > --
> > 2.7.4
> >