scsi: iscsi: Fix conn use after free during resets

If we haven't done a unbind target call we can race where
iscsi_conn_teardown wakes up the EH thread and then frees the conn while
those threads are still accessing the conn ehwait.

We can only do one TMF per session so this just moves the TMF fields from
the conn to the session. We can then rely on the
iscsi_session_teardown->iscsi_remove_session->__iscsi_unbind_session call
to remove the target and it's devices, and know after that point there is
no device or scsi-ml callout trying to access the session.

Link: https://lore.kernel.org/r/20210525181821.7617-14-michael.christie@oracle.comReviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

include/scsi/libiscsi.h

@@ -202,12 +202,6 @@ struct iscsi_conn {
 	unsigned long		suspend_tx;	/* suspend Tx */
 	unsigned long		suspend_rx;	/* suspend Rx */
 
-	/* abort */
-	wait_queue_head_t	ehwait;		/* used in eh_abort() */
-	struct iscsi_tm		tmhdr;
-	struct timer_list	tmf_timer;
-	int			tmf_state;	/* see TMF_INITIAL, etc.*/
-
 	/* negotiated params */
 	unsigned		max_recv_dlength; /* initiator_max_recv_dsl*/
 	unsigned		max_xmit_dlength; /* target_max_recv_dsl */
@@ -277,6 +271,11 @@ struct iscsi_session {
 	 * and recv lock.
 	 */
 	struct mutex		eh_mutex;
+	/* abort */
+	wait_queue_head_t	ehwait;		/* used in eh_abort() */
+	struct iscsi_tm		tmhdr;
+	struct timer_list	tmf_timer;
+	int			tmf_state;	/* see TMF_INITIAL, etc.*/
 
 	/* iSCSI session-wide sequencing */
 	uint32_t		cmdsn;