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virtio: hint if callbacks surprisingly might sleep

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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 <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
This commit is contained in:
Cornelia Huck 2019-01-31 13:53:14 +01:00 • committed by Michael S. Tsirkin
commit ab7a2375fb
2 changed files with 15 additions and 0 deletions
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2
drivers/virtio/virtio.c
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@ -161,6 +161,7 @@ EXPORT_SYMBOL_GPL(virtio_config_enable);
void virtio_add_status(struct virtio_device *dev, unsigned int status)
{
might_sleep();
dev->config->set_status(dev, dev->config->get_status(dev) | status);
}
EXPORT_SYMBOL_GPL(virtio_add_status);
@ -170,6 +171,7 @@ int virtio_finalize_features(struct virtio_device *dev)
int ret = dev->config->finalize_features(dev);
unsigned status;
might_sleep();
if (ret)
return ret;