scsi: libfc: Avoid invoking response handler twice if ep is already completed

A race condition exists between the response handler getting called because
of exchange_mgr_reset() (which clears out all the active XIDs) and the
response we get via an interrupt.

Sequence of events:

	 rport ba0200: Port timeout, state PLOGI
	 rport ba0200: Port entered PLOGI state from PLOGI state
	 xid 1052: Exchange timer armed : 20000 msecs      xid timer armed here
	 rport ba0200: Received LOGO request while in state PLOGI
	 rport ba0200: Delete port
	 rport ba0200: work event 3
	 rport ba0200: lld callback ev 3
	 bnx2fc: rport_event_hdlr: event = 3, port_id = 0xba0200
	 bnx2fc: ba0200 - rport not created Yet!!
	 /* Here we reset any outstanding exchanges before
	 freeing rport using the exch_mgr_reset() */
	 xid 1052: Exchange timer canceled
	 /* Here we got two responses for one xid */
	 xid 1052: invoking resp(), esb 20000000 state 3
	 xid 1052: invoking resp(), esb 20000000 state 3
	 xid 1052: fc_rport_plogi_resp() : ep->resp_active 2
	 xid 1052: fc_rport_plogi_resp() : ep->resp_active 2

Skip the response if the exchange is already completed.

Link: https://lore.kernel.org/r/20201215194731.2326-1-jhasan@marvell.com
Signed-off-by: Javed Hasan <jhasan@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: javed-h

drivers/scsi/libfc/fc_exch.c

@@ -1623,8 +1623,13 @@ static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
 		rc = fc_exch_done_locked(ep);
 		WARN_ON(fc_seq_exch(sp) != ep);
 		spin_unlock_bh(&ep->ex_lock);
-		if (!rc)
+		if (!rc) {
 			fc_exch_delete(ep);
+		} else {
+			FC_EXCH_DBG(ep, "ep is completed already,"
+					"hence skip calling the resp\n");
+			goto skip_resp;
+		}
 	}
 
 	/*
@@ -1643,6 +1648,7 @@ static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
 	if (!fc_invoke_resp(ep, sp, fp))
 		fc_frame_free(fp);
 
+skip_resp:
 	fc_exch_release(ep);
 	return;
 rel:
@@ -1899,10 +1905,16 @@ static void fc_exch_reset(struct fc_exch *ep)
 
 	fc_exch_hold(ep);
 
-	if (!rc)
+	if (!rc) {
 		fc_exch_delete(ep);
+	} else {
+		FC_EXCH_DBG(ep, "ep is completed already,"
+				"hence skip calling the resp\n");
+		goto skip_resp;
+	}
 
 	fc_invoke_resp(ep, sp, ERR_PTR(-FC_EX_CLOSED));
+skip_resp:
 	fc_seq_set_resp(sp, NULL, ep->arg);
 	fc_exch_release(ep);
 }