From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:55400)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <cota@braap.org>) id 1bmkBQ-0000V0-IH
	for qemu-devel@nongnu.org; Wed, 21 Sep 2016 12:15:41 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <cota@braap.org>) id 1bmkBJ-0005Mx-Tn
	for qemu-devel@nongnu.org; Wed, 21 Sep 2016 12:15:39 -0400
Received: from out2-smtp.messagingengine.com ([66.111.4.26]:51012)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <cota@braap.org>) id 1bmkBI-0005KA-Ae
	for qemu-devel@nongnu.org; Wed, 21 Sep 2016 12:15:33 -0400
Date: Wed, 21 Sep 2016 12:15:22 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20160921161522.GC13385@flamenco>
References: <1474289459-15242-1-git-send-email-pbonzini@redhat.com>
	<1474289459-15242-14-git-send-email-pbonzini@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1474289459-15242-14-git-send-email-pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 13/16] cpus-common: simplify locking for
 start_exclusive/end_exclusive
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, serge.fdrv@gmail.com, alex.bennee@linaro.org, sergey.fedorov@linaro.org

On Mon, Sep 19, 2016 at 14:50:56 +0200, Paolo Bonzini wrote:
> It is not necessary to hold qemu_cpu_list_mutex throughout the
> exclusive section, because no other exclusive section can run
> while pending_cpus != 0.
> 
> exclusive_idle() is called in cpu_exec_start(), and that prevents
> any CPUs created after start_exclusive() from entering cpu_exec()
> during an exclusive section.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  cpus-common.c              | 6 ++++++
>  docs/tcg-exclusive.promela | 4 +++-
>  include/qom/cpu.h          | 4 ----
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/cpus-common.c b/cpus-common.c
> index 9225c65..6adc982 100644
> --- a/cpus-common.c
> +++ b/cpus-common.c
> @@ -191,11 +191,17 @@ void start_exclusive(void)
>      if (pending_cpus > 1) {
>          qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_mutex);
>      }
> +
> +    /* Can release mutex, no one will enter another exclusive
> +     * section until end_exclusive resets pending_cpus to 0.
> +     */
> +    qemu_mutex_unlock(&qemu_cpu_list_mutex);
>  }
>  
>  /* Finish an exclusive operation.  Releases qemu_cpu_list_mutex.  */
>  void end_exclusive(void)
>  {
> +    qemu_mutex_lock(&qemu_cpu_list_mutex);
>      pending_cpus = 0;
>      qemu_cond_broadcast(&exclusive_resume);
>      qemu_mutex_unlock(&qemu_cpu_list_mutex);

The comments at the top of both start_exclusive and end_exclusive
should be updated.

		E.