Cornelia Huck
2019-Feb-13 13:44 UTC
[PATCH RFC] virtio: hint if callbacks surprisingly might sleep
On Thu, 31 Jan 2019 10:27:53 -0500 "Michael S. Tsirkin" <mst at 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 at 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.
Michael S. Tsirkin
2019-Feb-13 15:04 UTC
[PATCH RFC] virtio: hint if callbacks surprisingly might sleep
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 at 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 at 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!
Reasonably Related Threads
- [PATCH RFC] virtio: hint if callbacks surprisingly might sleep
- [PATCH RFC] virtio: hint if callbacks surprisingly might sleep
- [PATCH 2/2] virtio: document virtio_config_ops restrictions
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- [PATCH 0/2] virtio: virtio_config_ops documentation