ublk: add timeout handler

Add timeout handler, so that we can provide forward progress guarantee for
unprivileged ublk, which can't be trusted.

One thing is that sync() calls sync_bdevs(wait) for all block devices after
running sync_bdevs(no_wait), and if one device can't move on, the sync() won't
return any more.

Add timeout for unprivileged ublk to avoid such affect for other users which call
sync() syscall.

Meantime clear UBLK_F_USER_RECOVERY_REISSUE for unprivileged ublk since
that feature may cause IO hang too.

Fixes: 4093cb5a ("ublk_drv: add mechanism for supporting unprivileged ublk device")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230502024231.888498-1-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>