[PATCH v2 1/3] virtio: document virtio_reset_device

[PATCH v2 1/3] virtio: document virtio_reset_device

[Michael S. Tsirkin]

Looks like most callers get driver/device removal wrong.
Document what's expected of callers.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/virtio/virtio.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 2ed6e2451fd8..631a346a3aa6 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -201,6 +201,22 @@ static int virtio_finalize_features(struct virtio_device *dev)
 	return 0;
 }
 
+/**
+ * virtio_reset_device - quiesce device for removal
+ * @dev: the device to reset
+ *
+ * Prevents device from sending interrupts and accessing memory.
+ *
+ * Generally used for cleanup during driver / device removal.
+ *
+ * Once this has been invoked, caller must ensure that
+ * virtqueue_notify / virtqueue_kick are not in progress.
+ *
+ * Note: this guarantees that vq callbacks are not in progress, however caller
+ * is responsible for preventing access from other contexts, such as a system
+ * call/workqueue/bh.  Invoking virtio_break_device then flushing any such
+ * contexts is one way to handle that.
+ * */
 void virtio_reset_device(struct virtio_device *dev)
 {
 	dev->config->reset(dev);
-- 
MST

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[PATCH v2 2/3] virtio_console: break out of buf poll on remove

[Michael S. Tsirkin]

A common pattern for device reset is currently:
vdev->config->reset(vdev);
.. cleanup ..

reset prevents new interrupts from arriving and waits for interrupt
handlers to finish.

However if - as is common - the handler queues a work request which is
flushed during the cleanup stage, we have code adding buffers / trying
to get buffers while device is reset. Not good.

This was reproduced by running
	modprobe virtio_console
	modprobe -r virtio_console
in a loop.

Fix this up by calling virtio_break_device + flush before reset.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1786239
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/char/virtio_console.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 2359889a35a0..e3c430539a17 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1957,6 +1957,13 @@ static void virtcons_remove(struct virtio_device *vdev)
 	list_del(&portdev->list);
 	spin_unlock_irq(&pdrvdata_lock);
 
+	/* Device is going away, exit any polling for buffers */
+	virtio_break_device(vdev);
+	if (use_multiport(portdev))
+		flush_work(&portdev->control_work);
+	else
+		flush_work(&portdev->config_work);
+
 	/* Disable interrupts for vqs */
 	virtio_reset_device(vdev);
 	/* Finish up work that's lined up */
-- 
MST

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[PATCH v2 3/3] virtio_mem: break device on remove

[Michael S. Tsirkin]

A common pattern for device reset is currently:
vdev->config->reset(vdev);
.. cleanup ..

reset prevents new interrupts from arriving and waits for interrupt
handlers to finish.

However if - as is common - the handler queues a work request which is
flushed during the cleanup stage, we have code adding buffers / trying
to get buffers while device is reset. Not good.

This was reproduced by running
	modprobe virtio_console
	modprobe -r virtio_console
in a loop, and this reasoning seems to apply to virtio mem though
I could not reproduce it there.

Fix this up by calling virtio_break_device + flush before reset.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/virtio/virtio_mem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 38becd8d578c..33b8a118a3ae 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -2888,6 +2888,8 @@ static void virtio_mem_remove(struct virtio_device *vdev)
 		virtio_mem_deinit_hotplug(vm);
 
 	/* reset the device and cleanup the queues */
+	virtio_break_device(vdev);
+	flush_work(&vm->wq);
 	virtio_reset_device(vdev);
 	vdev->config->del_vqs(vdev);
 
-- 
MST

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