From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bart Van Assche <bvanassche@acm.org>
Subject: Re: [PATCH 2/2] vhost: Avoid that vhost_work_flush() returns early
Date: Wed, 14 Aug 2013 17:19:06 +0200
Message-ID: <520B9FEA.7090005@acm.org>
References: <520B2B47.9040002@acm.org> <520B2BC0.3050807@acm.org> <20130814114640.GG5430@redhat.com>
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Cc: Asias He <asias@redhat.com>, kvm-devel <kvm@vger.kernel.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
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On 08/14/13 13:46, Michael S. Tsirkin wrote:
> I'm confused by this explanation.
> done_seq is set here:
>                  if (work) {
>                          work->done_seq = seq;
>                          if (work->flushing)
>                                  wake_up_all(&work->done);
>                  }
>
> and work is set here:
>
>                  if (!list_empty(&dev->work_list)) {
>                          work = list_first_entry(&dev->work_list,
>                                                  struct vhost_work, node);
>                          list_del_init(&work->node);
>                          seq = work->queue_seq;
>                  }
>
> this work is processed on the next line:
>
>                  if (work) {
>                          __set_current_state(TASK_RUNNING);
>                          work->fn(work);
>                          if (need_resched())
>                                  schedule();
>                  }
>
> so how do we end up with a sequence of a work item
> that isn't processed?

I was wondering what would happen if a work item got requeued before 
done_seq is set. I think you are right and this should work fine.

Bart.