On 2021/1/20 下午2:52, Yongji Xie wrote:
On Wed, Jan 20, 2021 at 12:24 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
On 2021/1/19 下午12:59, Xie Yongji wrote:
Now we have a global percpu counter to limit the recursion depth
of eventfd_signal(). This can avoid deadlock or stack overflow.
But in stack overflow case, it should be OK to increase the
recursion depth if needed. So we add a percpu counter in eventfd_ctx
to limit the recursion depth for deadlock case. Then it could be
fine to increase the global percpu counter later.
I wonder whether or not it's worth to introduce percpu for each eventfd.
How about simply check if eventfd_signal_count() is greater than 2?
It can't avoid deadlock in this way.
I may miss something but the count is to avoid recursive eventfd call.
So for VDUSE what we suffers is e.g the interrupt injection path:
userspace write IRQFD -> vq->cb() -> another IRQFD.
It looks like increasing EVENTFD_WAKEUP_DEPTH should be sufficient?
Thanks
So we need a percpu counter for
each eventfd to limit the recursion depth for deadlock cases. And
using a global percpu counter to avoid stack overflow.
Thanks,
Yongji
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