lkml.org 
[lkml]   [2019]   [Jan]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] virtio: document virtio_config_ops restrictions
On Thu, 3 Jan 2019 18:28:49 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Thu, 3 Jan 2019 17:08:04 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
>
> > Some transports (e.g. virtio-ccw) implement virtio operations that
> > seem to be a simple read/write as something more involved that
> > cannot be done from an atomic context.
> >
> > Give at least a hint about that.
> >
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> > include/linux/virtio_config.h | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index 7087ef946ba7..987b6491b946 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -12,6 +12,11 @@ struct irq_affinity;
> >
> > /**
> > * virtio_config_ops - operations for configuring a virtio device
> > + * Note: Do not assume that a transport implements all of the operations
> > + * getting/setting a value as a simple read/write! Generally speaking,
> > + * any of @get/@set, @get_status/@set_status, or @get_features/
> > + * @finalize_features are NOT safe to be called from an atomic
> > + * context.
>
> I think the only exception is @bus_name (and maybe @generation, I don't
> know) because it does not have to 'speak' with the hypervisor. If a
> transport operation has to 'speak' with the hypervisor, we do it by
> making it interpret a channel program. That means not safe to be called
> form atomic context. Or am I missing something?

I explicitly singled out the listed callbacks because they read/write a
value and there might be more to them than meets the eye. I would
assume that nobody expects calling e.g. find_vqs (allocating queues)
from an atomic context to be a good idea :) Maybe I should do
s/Generally speaking/In particular/ ?

That said, it's only a hint; we should add might_sleep as well to
interfaces where it makes sense.

\
 
 \ /
  Last update: 2019-01-04 13:49    [W:0.110 / U:2.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site