Re: [Qemu-devel] [PATCH v2 1/1] coroutine-lock: do not touch coroutine after another one has been entered

[Stefan Hajnoczi]

On Tue, May 30, 2017 at 12:07:36PM +0200, Roman Pen wrote:
> diff --git a/util/qemu-coroutine-lock.c b/util/qemu-coroutine-lock.c
> index 6328eed26bc6..d589d8c66d5e 100644
> --- a/util/qemu-coroutine-lock.c
> +++ b/util/qemu-coroutine-lock.c
> @@ -77,10 +77,20 @@ void coroutine_fn qemu_co_queue_wait(CoQueue *queue, 
> CoMutex *mutex)
>  void qemu_co_queue_run_restart(Coroutine *co)
>  {
>      Coroutine *next;
> +    QSIMPLEQ_HEAD(, Coroutine) tmp_queue_wakeup =
> +        QSIMPLEQ_HEAD_INITIALIZER(tmp_queue_wakeup);
>  
>      trace_qemu_co_queue_run_restart(co);
> -    while ((next = QSIMPLEQ_FIRST(&co->co_queue_wakeup))) {
> -        QSIMPLEQ_REMOVE_HEAD(&co->co_queue_wakeup, co_queue_next);
> +
> +    /* Because "co" has yielded, any coroutine that we wakeup can resume it.
> +     * If this happens and "co" terminates, co->co_queue_wakeup becomes
> +     * invalid memory.  Therefore, use a temporary queue and do not touch
> +     * the "co" coroutine as soon as you enter another one.
> +     */
> +    QSIMPLEQ_CONCAT(&tmp_queue_wakeup, &co->co_queue_wakeup);
> +
> +    while ((next = QSIMPLEQ_FIRST(&tmp_queue_wakeup))) {
> +        QSIMPLEQ_REMOVE_HEAD(&tmp_queue_wakeup, co_queue_next);
>          qemu_coroutine_enter(next);
>      }
>  }

What happens if co remains alive and qemu_coroutine_enter(next) causes
additional coroutines to add themselves to co->co_queue_wakeup?

I think they used to be entered but not anymore after this patch.  Not
sure if anything depends on this behavior...

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