On 2022-06-02 10:30, Jason Gunthorpe wrote: > On Thu, Jun 02, 2022 at 10:16:10AM -0600, Logan Gunthorpe wrote: > >>> Just stuff the pages into the mmap, and your driver unprobe will >>> automatically block until all the mmaps are closed - no different than >>> having an open file descriptor or something. >> >> Oh is that what we want? > > Yes, it is the typical case - eg if you have a sysfs file open unbind > hangs indefinitely. Many drivers can't unbind while they have open file > descriptors/etc. > > A couple drivers go out of their way to allow unbinding while a live > userspace exists but this can get complicated. Usually there should be > a good reason. This is not my experience. All the drivers I've worked with do not block unbind with open file descriptors (at least for char devices). I know, for example, that having a file descriptor open of /dev/nvmeX does not cause unbinding to block. I figured this was the expectation as the userspace process doing the unbind won't be able to be interrupted seeing there's no way to fail on that path. Though, it certainly would make things a lot easier if the unbind can block indefinitely as it usually requires some complicated locking. Do you have an example of this? What mechanisms are developers using to block unbind with open file descriptors? Logan
