scsi: lpfc: Unsolicited ELS leaves node in incorrect state while dropping it

scsi: lpfc: Unsolicited ELS leaves node in incorrect state while dropping it

When a target swap happens, under certain conditions the node sends a
LOGO. The unsolicited ELS logic responds with a reject. The logic may
allocate a new node to handle this. Afterward, the new nodes are dropped
incorrectly leaving them in a mis-matched state and refcounting causes a
use-after-free situation leading to a crash.

It is also possible that the unsolicited els handling finds a node which is
in an UNUSED state. The handling moves these nodes to NPR state with a
refcount of 1. Although the end of the discovery logic assumes a final put
will free such a node, there are codes paths which could increment the
reference count, thus the node is in NPR state and not released.
Eventually this mismatch in state and refcount leads to premature release
of the node causing a crash.

Fix by always using the discovery engine DEVICE RM event to decrement and
release the nodes (rather than explicit code that tried to do it before).
This will take care of moving the node to the UNUSED state and then removes
the final ref count. If there is a trigger to reuse this node, the
transition from the UNUSED state clearly indicates that the initial
reference is then incremented and use can continue.

Link: https://lore.kernel.org/r/20201115192646.12977-8-james.smart@broadcom.com
Co-developed-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>