libfc: Fix fc_exch_recv_req() error path

Due to patch "libfc: Do not invoke the response handler after
fc_exch_done()" (commit ID 7030fd62) the lport_recv() call
in fc_exch_recv_req() is passed a dangling pointer. Avoid this
by moving the fc_frame_free() call from fc_invoke_resp() to its
callers. This patch fixes the following crash:

general protection fault: 0000 [#3] PREEMPT SMP
RIP: fc_lport_recv_req+0x72/0x280 [libfc]
Call Trace:
 fc_exch_recv+0x642/0xde0 [libfc]
 fcoe_percpu_receive_thread+0x46a/0x5ed [fcoe]
 kthread+0x10a/0x120
 ret_from_fork+0x42/0x70

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

drivers/scsi/libfc/fc_exch.c

@@ -733,8 +733,6 @@ static bool fc_invoke_resp(struct fc_exch *ep, struct fc_seq *sp,
 	if (resp) {
 		resp(sp, fp, arg);
 		res = true;
-	} else if (!IS_ERR(fp)) {
-		fc_frame_free(fp);
 	}
 
 	spin_lock_bh(&ep->ex_lock);
@@ -1596,7 +1594,8 @@ static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
 	 * If new exch resp handler is valid then call that
 	 * first.
 	 */
-	fc_invoke_resp(ep, sp, fp);
+	if (!fc_invoke_resp(ep, sp, fp))
+		fc_frame_free(fp);
 
 	fc_exch_release(ep);
 	return;
@@ -1695,7 +1694,8 @@ static void fc_exch_abts_resp(struct fc_exch *ep, struct fc_frame *fp)
 	fc_exch_hold(ep);
 	if (!rc)
 		fc_exch_delete(ep);
-	fc_invoke_resp(ep, sp, fp);
+	if (!fc_invoke_resp(ep, sp, fp))
+		fc_frame_free(fp);
 	if (has_rec)
 		fc_exch_timer_set(ep, ep->r_a_tov);
 	fc_exch_release(ep);