Re: [PATCH RFC] virtio: hint if callbacks surprisingly might sleep

Michael S. Tsirkin
2019-02-13T15:04:49Z

On Wed, Feb 13, 2019 at 02:44:14PM +0100, Cornelia Huck wrote:
> On Thu, 31 Jan 2019 10:27:53 -0500
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>
> > On Thu, Jan 31, 2019 at 01:53:14PM +0100, Cornelia Huck wrote:
> > > A virtio transport is free to implement some of the callbacks in
> > > virtio_config_ops in a matter that they cannot be called from
> > > atomic context (e.g. virtio-ccw, which maps a lot of the callbacks
> > > to channel I/O, which is an inherently asynchronous mechanism).
> > > This can be very surprising for developers using the much more
> > > common virtio-pci transport, just to find out that things break
> > > when used on s390.
> > >
> > > The documentation for virtio_config_ops now contains a comment
> > > explaining this, but it makes sense to add a might_sleep() annotation
> > > to various wrapper functions in the virtio core to avoid surprises
> > > later.
> > >
> > > Note that annotations are NOT added to two classes of calls:
> > > - direct calls from device drivers (all current callers should be
> > > fine, however)
> > > - calls which clearly won't be made from atomic context (such as
> > > those ultimately coming in via the driver core)
> > >
> > > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> >
> >
> > Makes sense to me. I don't think we should push our luck in
> > this release though, better defer until the merge window.
>
> Friendly ping, as we're quite close to the release of 5.0 now.

Queued now, thanks!