From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:36892)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <fred.konrad@greensocs.com>) id 1ZDaSr-0003oo-AU
	for qemu-devel@nongnu.org; Fri, 10 Jul 2015 11:43:50 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <fred.konrad@greensocs.com>) id 1ZDaSn-0004V1-TV
	for qemu-devel@nongnu.org; Fri, 10 Jul 2015 11:43:49 -0400
Received: from greensocs.com ([193.104.36.180]:60803)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <fred.konrad@greensocs.com>) id 1ZDaSn-0004US-Mw
	for qemu-devel@nongnu.org; Fri, 10 Jul 2015 11:43:45 -0400
Message-ID: <559FE829.6090001@greensocs.com>
Date: Fri, 10 Jul 2015 17:43:37 +0200
From: Frederic Konrad <fred.konrad@greensocs.com>
MIME-Version: 1.0
References: <1436541553-26576-1-git-send-email-fred.konrad@greensocs.com>
	<1436541553-26576-2-git-send-email-fred.konrad@greensocs.com>
	<559FE32C.5030609@redhat.com> <559FE58C.6040400@greensocs.com>
	<559FE600.7040500@redhat.com>
In-Reply-To: <559FE600.7040500@redhat.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [RFC PATCH 1/3] cpus: protect queued_work_* with
	work_mutex.
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>, qemu-devel@nongnu.org, mttcg@greensocs.com
Cc: mark.burton@greensocs.com, alex.bennee@linaro.org, a.rigo@virtualopensystems.com, guillaume.delbergue@greensocs.com

On 10/07/2015 17:34, Paolo Bonzini wrote:
>
> On 10/07/2015 17:32, Frederic Konrad wrote:
>> I think something like that can work because we don't have two
>> flush_queued_work at the same time on the same CPU?
> Yes, this works; there is only one consumer.
>
> Holding locks within a callback can be very painful, especially if there
> is a chance that the callback will take a very coarse lock such as big
> QEMU lock.  It can cause AB-BA deadlocks.
>
> Paolo

Ok fine I'll change that.

Fred
>
>> static void flush_queued_work(CPUState *cpu)
>> {
>>      struct qemu_work_item *wi;
>>
>>      if (cpu->queued_work_first == NULL) {
>>          return;
>>      }
>>
>>      qemu_mutex_lock(&cpu->work_mutex);
>>      while ((wi = cpu->queued_work_first)) {
>>          cpu->queued_work_first = wi->next;
>>          qemu_mutex_unlock(&cpu->work_mutex);
>>          wi->func(wi->data);
>>          qemu_mutex_lock(&cpu->work_mutex);
>>          wi->done = true;
>>          if (wi->free) {
>>              g_free(wi);
>>          }
>>      }
>>      cpu->queued_work_last = NULL;
>>      qemu_mutex_unlock(&cpu->work_mutex);
>>
>>      qemu_cond_broadcast(&qemu_work_cond);
>> }