Re: [Qemu-devel] [RFC v3 0/3] scsi: restart dma after vm change state handlers

[Paolo Bonzini]

On 24/05/19 20:36, Stefan Hajnoczi wrote:
> v3:
>  * Fix s/k->vmstate_change/vdc->vmstate_change/
>  * Still RFC, waiting for customer to confirm this fixes the issue
> v2:
>  * Do it properly with a clean API instead of deferring to a BH!
>    Thanks for encouraging me to do this, Kevin.
> 
> These patches solve a deadlock when the 'cont' command is used and there are
> failed requests on a virtio-scsi device with iothreads.  The deadlock itself 
> is
> actually not the thing we need to fix because we should never reach that case
> anyway.  Instead we need to make sure DMA restart is only performed after the
> virtio-scsi iothread is re-initialized.

custom_dma_restart is a bit ugly...  Do you think it would make sense to
order the VMStateChange handlers using some kind of enum (with the order
unspecified within the category)?

We could start with

        VMSTATECHANGE_PRIO_UNKNOWN  = 0  (if needed?)
        VMSTATECHANGE_PRIO_IOTHREAD = 100
        VMSTATECHANGE_PRIO_DEVICE   = 200

where higher priorities run first on stop and last on resume.

Paolo