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Date: Wed, 21 Sep 2016 13:37:26 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20160921173726.GA27412@flamenco>
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Subject: Re: [Qemu-devel] [PATCH 15/16] tcg: Make tb_flush() thread safe
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, serge.fdrv@gmail.com, alex.bennee@linaro.org, sergey.fedorov@linaro.org

On Wed, Sep 21, 2016 at 18:19:26 +0200, Paolo Bonzini wrote:
> 
> 
> On 21/09/2016 18:05, Emilio G. Cota wrote:
> >> > +    tb_lock();
> >> > +
> >> > +    /* If it's already been done on request of another CPU,
> >> > +     * just retry.
> >> > +     */
> >> > +    if (atomic_read(&tcg_ctx.tb_ctx.tb_flush_count) != tb_flush_req) {
> >> > +        goto done;
> > tb_flush_count is always accessed with tb_lock held, right? If so, I don't
> > see a reason to access it with atomic_read/set.
> 
> tb_flush accesses it outside tb_lock.  Technically this one you're
> quoting need not use atomic_read, but others need to.

Sorry for being thick, but when does tb_flush not own tb_lock?
(I'm assuming we're talking only user-mode, since full-system has
for now empty tb_lock/unlock helpers.)

		E.