Re: [PATCH] xen-bus/block: explicitly assign event channels to an AioContext

[Anthony PERARD <anthony.perard@citrix.com>]

On Mon, Dec 16, 2019 at 02:34:51PM +0000, Paul Durrant wrote:
> It is not safe to close an event channel from the QEMU main thread when
> that channel's poller is running in IOThread context.
> 
> This patch adds a new xen_device_set_event_channel_context() function
> to explicitly assign the channel AioContext, and modifies
> xen_device_bind_event_channel() to initially assign the channel's poller
> to the QEMU main thread context. The code in xen-block's dataplane is
> then modified to assign the channel to IOThread context during
> xen_block_dataplane_start() and de-assign it during in
> xen_block_dataplane_stop(), such that the channel is always assigned
> back to main thread context before it is closed. aio_set_fd_handler()
> already deals with all the necessary synchronization when moving an fd
> between AioContext-s so no extra code is needed to manage this.
> 
> Reported-by: Julien Grall <jgrall@amazon.com>
> Signed-off-by: Paul Durrant <pdurrant@amazon.com>

Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

> Tested against an HVM debian guest with a QCOW2 image as system disk, and
> as a hot-plugged/unplgged secondary disk.

And I've run an osstest flight with the patch.

Thanks,

-- 
Anthony PERARD