scsi: iscsi: Fix deadlock on recovery path during GFP_IO reclaim

      iSCSI suffers from a deadlock in case a management command submitted via
the netlink socket sleeps on an allocation while holding the rx_queue_mutex
if that allocation causes a memory reclaim that writebacks to a failed
iSCSI device.  The recovery procedure can never make progress to recover
the failed disk or abort outstanding IO operations to complete the reclaim
(since rx_queue_mutex is locked), thus locking the system.

Nevertheless, just marking all allocations under rx_queue_mutex as GFP_NOIO
(or locking the userspace process with something like PF_MEMALLOC_NOIO) is
not enough, since the iSCSI command code relies on other subsystems that
try to grab locked mutexes, whose threads are GFP_IO, leading to the same
deadlock. One instance where this situation can be observed is in the
backtraces below, stitched from multiple bugs reports, involving the kobj
uevent sent when a session is created.

The root of the problem i