device-assignment deadlock

device-assignment deadlock

[Alex Williamson]

Hi Sheng,

I think I'm running into the following deadlock in the kvm kernel module
when trying to use device assignment:

CPU A                               CPU B
kvm_vm_ioctl_deassign_dev_irq()
  mutex_lock(&kvm->lock);           worker_thread()
  -> kvm_deassign_irq()               -> kvm_assigned_dev_interrupt_work_handler()
    -> deassign_host_irq()              mutex_lock(&kvm->lock);
      -> cancel_work_sync() [blocked]

I wonder if we need finer granularity locking to avoid this.
Suggestions?  Thanks,

Alex

Re: device-assignment deadlock

[Yang, Sheng]

[I was kicked off from the mailing list by periodic unknown reason last 
Friday... Sorry]

> Hi Sheng,
>
> I think I'm running into the following deadlock in the kvm kernel module
> when trying to use device assignment:
>
> CPU A                               CPU B
> kvm_vm_ioctl_deassign_dev_irq()
>  mutex_lock(&kvm->lock);           worker_thread()
>  -> kvm_deassign_irq()               -> 
>kvm_assigned_dev_interrupt_work_handler()
>    -> deassign_host_irq()              mutex_lock(&kvm->lock);
>      -> cancel_work_sync() [blocked]

> I wonder if we need finer granularity locking to avoid this.
> Suggestions?  Thanks,

This part again...

I think simply move kvm_deassign_irq() out of critical region is OK, and I 
also add the lock which seems missing in deassign_guest_irq(). Would post a 
patch soon.

-- 
regards
Yang, Sheng