On Wed, Mar 04, 2020 at 06:29:07PM +0100, Greg KH wrote: > The rule should be, "whenever you pass a pointer to a device off, the > reference count is incremented". Somehow that is not happening here and > RCU is not going to solve the issue really, it's only going to delay the > problem from showing up until much later. > ... > The struct device refcount should be all that is needed, don't use RCU > just to "delay freeing this object until some later time because someone > else might have a pointer to id". That's ripe for disaster. I agree that this is a better fix than trying to continue to paper over the problem. That being said, I also think it would be better if we could *also* send a notification to the file system (or device mapper) when a block device has disappeared, so we can set a flag in struct super indicating, "this is an ex-device" so that we don't have to have potentially hundreds of I/O errors clogging up the console and/or any error notification ifrastructure we might want to add in the future, as we attempt to send I/O to a device is not coming back. This would allow us to short-circuit things like writeback, instead of letting everything drain via pointless io_submits sending bios that will never go anywhere useful. - Ted
