If an nvme device is removed but user space has an open reference,
the nvme driver would have been holding an invalid reference to its pci
device. You may get a general protection fault on x86 h/w when the driver
uses that reference in dma_map_sg(), as is done in nvme_map_user_pages()
from the IOCTL interface.
This patch fixes the fault by taking a reference on the pci device and
holding it even after device removal until all opens on the nvme device
are closed.
Signed-off-by: Keith Busch <keith.busch@intel.com> Reported-by: Nilesh Choudhury <nilesh.choudhury@oracle.com> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com> Signed-off-by: Jens Axboe <axboe@fb.com>