On 2022-06-02 10:30, Jason Gunthorpe wrote:

On Thu, Jun 02, 2022 at 10:16:10AM -0600, Logan Gunthorpe wrote:

quoted

quoted

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.

The module will already be refcounted anyhow because the mmap points
to a char file which holds a module reference - meaning a simple rmmod
of the driver shouldn't work already..

Also, I just tried it... If I open a sysfs file for an nvme device (ie.
/sys/class/nvme/nvme4/cntlid) and unbind the device, it does not block.
A subsequent read on that file descriptor returns ENODEV. Which is what
I would have expected.

Logan