scsi: core: Restrict legal sdev_state transitions via sysfs

scsi: core: Restrict legal sdev_state transitions via sysfs

Userspace can currently write to sysfs to transition sdev_state to RUNNING
or OFFLINE from any source state. This causes issues because proper
transitioning out of some states involves steps besides just changing
sdev_state, so allowing userspace to change sdev_state regardless of the
source state can result in inconsistencies; e.g. with ISCSI we can end up
with sdev_state == SDEV_RUNNING while the device queue is quiesced. Any
task attempting I/O on the device will then hang, and in more recent
kernels, iscsid will hang as well.

More detail about this bug is provided in my first attempt:

https://groups.google.com/g/open-iscsi/c/PNKca4HgPDs/m/CXaDkntOAQAJ

Link: https://lore.kernel.org/r/20220924000241.2967323-1-ushankar@purestorage.com
Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Suggested-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>