[PATCH RFC] pci: report surprise removal events

["Michael S. Tsirkin" <mst@redhat.com>]

At the moment, in case of a surprise removal, the regular
remove callback is invoked, exclusively.
This works well, because mostly, the cleanup would be the same.

However, there's a race: imagine device removal was initiated by a user
action, such as driver unbind, and it in turn initiated some cleanup and
is now waiting for an interrupt from the device. If the device is now
surprise-removed, that never arrives and the remove callback hangs
forever.

Drivers can artificially add timeouts to handle that, but it can be
flaky.

Instead, let's add a way for the driver to be notified about the
disconnect. It can then do any necessary cleanup, knowing that the
device is inactive.

Given this is by design kind of asynchronous with normal probe/remove
callbacks, I added it in the pci_error_handlers callback.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Warning: build-tested only at this point.

Posting for early flames/feedback.

Cc a bunch of people who discussed this problem specifically in the
virtio blk driver.

 drivers/pci/pci.h   | 9 +++++++++
 include/linux/pci.h | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index b81e99cd4b62..78b064be10d5 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -549,6 +549,15 @@ static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
 	pci_dev_set_io_state(dev, pci_channel_io_perm_failure);
 	pci_doe_disconnected(dev);
 
+	/* Notify driver of surprise removal */
+	device_lock(&dev->dev);
+
+	if (dev->driver && dev->driver->err_handler &&
+	    dev->driver->err_handler->disconnect)
+		dev->driver->err_handler->disconnect(dev);
+
+	device_unlock(&dev->dev);
+
 	return 0;
 }
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 51e2bd6405cd..30a8c7ee09f6 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -878,6 +878,9 @@ struct pci_error_handlers {
 	/* PCI slot has been reset */
 	pci_ers_result_t (*slot_reset)(struct pci_dev *dev);
 
+	/* PCI slot has been disconnected */
+        void (*disconnect)(struct pci_dev *dev);
+
 	/* PCI function reset prepare or completed */
 	void (*reset_prepare)(struct pci_dev *dev);
 	void (*reset_done)(struct pci_dev *dev);
-- 
MST