s390/pci: Prevent self deletion in disable_slot()

As disable_slot() takes a struct zpci_dev from the Configured to the
Standby state. In Standby there is still a hotplug slot so this is not
usually a case of sysfs self deletion. This is important because self
deletion gets very hairy in terms of locking (see for example
recover_store() in arch/s390/pci/pci_sysfs.c).

Because the pci_dev_put() is not within the critical section of the
zdev->state_lock however, disable_slot() can turn into a case of self
deletion if zPCI device event handling slips between the mutex_unlock()
and the pci_dev_put(). If the latter is the last put and
zpci_release_device() is called this then tries to remove the hotplug
slot via zpci_exit_slot() which will try to remove the hotplug slot
directory the disable_slot() is part of i.e. self deletion.

Prevent this by widening the zdev->state_lock critical section to
include the pci_dev_put() which is then guaranteed to happen with the
struct zpci_dev still in Standby state ensuring it will not lead to
a zpci_release_device() call as at least the zPCI event handling code
still holds a reference.

Cc: [email protected]
Fixes: a46044a ("s390/pci: fix zpci_zdev_put() on reserve")
Reviewed-by: Gerd Bayer <[email protected]>
Tested-by: Gerd Bayer <[email protected]>
Signed-off-by: Niklas Schnelle <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>

Author: niklas88

drivers/pci/hotplug/s390_pci_hpc.c

@@ -66,9 +66,9 @@ static int disable_slot(struct hotplug_slot *hotplug_slot)
 
 	rc = zpci_deconfigure_device(zdev);
 out:
-	mutex_unlock(&zdev->state_lock);
 	if (pdev)
 		pci_dev_put(pdev);
+	mutex_unlock(&zdev->state_lock);
 	return rc;
 }