IB/umad: Return EPOLLERR in case of when device disassociated

IB/umad: Return EPOLLERR in case of when device disassociated

[ Upstream commit def4cd43f522253645b72c97181399c241b54536 ]

Currently, polling a umad device will always works, even if the device was
disassociated. A disassociated device should immediately return EPOLLERR
from poll(). Otherwise userspace is endlessly hung on poll() with no idea
that the device has been removed from the system.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/r/20210125121339.837518-3-leon@kernel.org
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>