pci: report surprise removal event
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.
For example, this was reported for virtio-blk:
1. the graceful removal is ongoing in the remove() callback, where disk
deletion del_gendisk() is ongoing, which waits for the requests +to
complete,
2. Now few requests are yet to complete, and surprise removal started.
At this point, virtio block driver will not get notified by the driver
core layer, because it is likely serializing remove() happening by
+user/driver unload and PCI hotplug driver-initiated device removal. So
vblk driver doesn't know that device is removed, block layer is waiting
for requests completions to arrive which it never gets. So
del_gendisk() gets stuck.
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.
Since cleanups can take a long time, this takes an approach
of a work struct that the driver initiates and enables
on probe, and tears down on remove.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2 files changed
