Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal()

[Paolo Bonzini]

On 16/07/21 11:37, Hillf Danton wrote:
> On Fri, 16 Jul 2021 09:59:15 +0200 Paolo Bonzini wrote:
> > * the warning only occurs if preemption occurs during the
> > spin_lock_irqsave critical section (and therefore it can only occur in
> > PREEMPT_RT kernels)
>
> With that lock held, no waitqueue entry can be added on to the WQ - IOW no
> wakeup will go stray.
>
> > * the warning causes an early return 0 that messes up the VM's networking
>
> Is the messup due to the zero or wakeup?

It's caused by the missing wakeup, i.e. eventfd_signal not really 
signaling anything.

Paolo