Re: [PATCH 0/9] vhost: Support SIGKILL by flushing and exiting

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 09, 2024 at 09:57:00AM -0500, Mike Christie wrote:
> On 4/8/24 11:16 PM, Jason Wang wrote:
> >> It turns out only vhost-scsi had an issue where it would send a command
> >> to the block/LIO layer, wait for a response and then process in the vhost
> >> task.
> > Vhost-net TX zerocopy code did the same:
> > 
> > It sends zerocopy packets to the under layer and waits for the
> > underlayer. When the DMA is completed, vhost_zerocopy_callback will be
> > called to schedule vq work for used ring updating.
> 
> I think it might be slightly different and vhost-net is ok.
> 
> Above I meant, vhost-scsi would do the equivalent of:
> 
> vhost_zerocopy_callback ->  vhost_net_ubuf_put
> 
> from vhost_task/thread.
> 
> For vhost-net then, if we get an early exit via a signal the patches will flush
> queued works and prevent new ones from being queued. vhost_net_release will run
> due to the process/thread exit code releasing it's refcounts on the device.
> 
> vhost_net_release will then do:
> 
> vhost_net_flush -> vhost_net_ubuf_put_and_wait
> 
> and wait for vhost_zerocopy_callback -> vhost_net_ubuf_put calls.
> 
> For vhost-scsi we would hang. We would do our equivalent of vhost_net_ubuf_put
> from the vhost task/thread. So, when our release function, vhost_scsi_release,
> is called we will also do a similar wait. However, because the task/thread is
> killed, we will hang there since the "put" will never be done.

If you can find a way to cancel them instead of flushing out,
I think it would be better for net, too.

-- 
MST