Re: [Qemu-devel] [BUG] VM abort after migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* longpeng (longpeng2@huawei.com) wrote:
> Hi guys,
> 
> We found a qemu core in our testing environment, the assertion
> 'assert(bus->irq_count[i] == 0)' in pcibus_reset() was triggered and
> the bus->irq_count[i] is '-1'.
> 
> Through analysis, it was happened after VM migration and we think
> it was caused by the following sequence:
> 
> *Migration Source*
> 1. save bus pci.0 state, including irq_count[x] ( =0 , old )
> 2. save E1000:
>    e1000_pre_save
>     e1000_mit_timer
>      set_interrupt_cause
>       pci_set_irq --> update pci_dev->irq_state to 1 and
>                   update bus->irq_count[x] to 1 ( new )
>     the irq_state sent to dest.
> 
> *Migration Dest*
> 1. Receive the irq_count[x] of pci.0 is 0 , but the irq_state of e1000 is 1.
> 2. If the e1000 need change irqline , it would call to pci_irq_handler(),
>   the irq_state maybe change to 0 and bus->irq_count[x] will become
>   -1 in this situation.
> 3. do VM reboot then the assertion will be triggered.
> 
> We also found some guys faced the similar problem:
> [1] https://lists.gnu.org/archive/html/qemu-devel/2016-11/msg02525.html
> [2] https://bugs.launchpad.net/qemu/+bug/1702621
> 
> Is there some patches to fix this problem ?

I don't remember any.

> Can we save pcibus state after all the pci devs are saved ?

Does this problem only happen with e1000? I think so.
If it's only e1000 I think we should fix it - I think once the VM is
stopped for doing the device migration it shouldn't be raising
interrupts.

Dave

> Thanks,
> Longpeng(Mike)
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK