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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 10 Jul 2015 17:34:24 +0200
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Subject: Re: [Qemu-devel] [RFC PATCH 1/3] cpus: protect queued_work_* with
	work_mutex.
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To: Frederic Konrad <fred.konrad@greensocs.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 17:32, 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

> 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);
> }