scsi: iscsi: Fix endpoint reuse regression

scsi: iscsi: Fix endpoint reuse regression

This patch fixes a bug where when using iSCSI offload we can free an
endpoint while userspace still thinks it's active. That then causes the
endpoint ID to be reused for a new connection's endpoint while userspace
still thinks the ID is for the original connection. Userspace will then end
up disconnecting a running connection's endpoint or trying to bind to
another connection's endpoint.

This bug is a regression added in:

Commit 23d6fefbb3f6 ("scsi: iscsi: Fix in-kernel conn failure handling")

where we added a in kernel ep_disconnect call to fix a bug in:

Commit 0ab710458da1 ("scsi: iscsi: Perform connection failure entirely in
kernel space")

where we would call stop_conn without having done ep_disconnect. This early
ep_disconnect call will then free the endpoint and it's ID while userspace
still thinks the ID is valid.

Fix the early release of the ID by having the in kernel recovery code keep
a reference to the endpoint until userspace has called into the kernel to
finish cleaning up the endpoint/connection. It requires the previous commit
"scsi: iscsi: Release endpoint ID when its freed" which moved the freeing
of the ID until when the endpoint is released.

Link: https://lore.kernel.org/r/20220408001314.5014-5-michael.christie@oracle.com
Fixes: 23d6fefbb3f6 ("scsi: iscsi: Fix in-kernel conn failure handling")
Tested-by: Manish Rangankar <mrangankar@marvell.com>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>