On Fri, 21 Feb 2014, Liu, Chuansheng wrote:
> But feels there is another case which the synchronize_irq waited there
> forever,
> it is no waking up action from irq_thread().
>
> CPU0 CPU1
> disable_irq() irq_thread()
> synchronize_irq()
> wait_event()
> adding the __wait into the queue wake_threads_waitq
> test threads_active==0
> atomic_dec_and_test(threads_active) 1
> -- > 0
>
> waitqueue_active(&desc->wait_for_threads)
> <== Here without smp_mb(), CPU1 maybe detect
> the queue is still empty??
> schedule()
>
> It will cause although the threads_active is 0, but irq_thread() didn't do
> the waking up action.
> Is it reasonable? Then maybe we can add one smp_mb() before waitqueue_active.
I think you have a point there, but not on x86 wherre the atomic_dec
and the spinlock on the queueing side are full barriers. For non-x86
there is definitely a potential issue.
Thanks,
tglx
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