scsi: libfc: Skip additional kref updating work event

When an rport event (RPORT_EV_READY) is updated without work being queued,
avoid taking an additional reference.

This issue was leading to memory leak. Trace from KMEMLEAK tool:

  unreferenced object 0xffff8888259e8780 (size 512):
  comm "kworker/2:1", jiffies 4433237386 (age 113021.971s)
    hex dump (first 32 bytes):
	58 0a ec cf 83 88 ff ff 00 00 00 00 00 00 00 00
	01 00 00 00 08 00 00 00 13 7d f0 1e 0e 00 00 10
  backtrace:
  [<000000006b25760f>] fc_rport_recv_req+0x3c6/0x18f0 [libfc]
  [<00000000f208d994>] fc_lport_recv_els_req+0x120/0x8a0 [libfc]
  [<00000000a9c437b8>] fc_lport_recv+0xb9/0x130 [libfc]
  [<00000000a9c437b8>] fc_lport_recv+0xb9/0x130 [libfc]
  [<00000000ad5be37b>] qedf_ll2_process_skb+0x73d/0xad0 [qedf]
  [<00000000e0eb6893>] process_one_work+0x382/0x6c0
  [<000000002dfd9e21>] worker_thread+0x57/0x5c0
  [<00000000b648204f>] kthread+0x1a0/0x1c0
  [<0000000072f5ab20>] ret_from_fork+0x35/0x40
  [<000000001d5c05d8>] 0xffffffffffffffff

Below is the log sequence which leads to memory leak.  Here we get the
RPORT_EV_READY and RPORT_EV_STOP back to back, which lead to overwrite the
event RPORT_EV_READY by event RPORT_EV_STOP.  Because of this, kref_count
gets incremented by 1.

  kernel: host0: rport fffce5: Received PLOGI request
  kernel: host0: rport fffce5: Received PLOGI in INIT state
  kernel: host0: rport fffce5: Port is Ready
  kernel: host0: rport fffce5: Received PRLI request while in state Ready
  kernel: host0: rport fffce5: PRLI rspp type 8 active 1 passive 0
  kernel: host0: rport fffce5: Received LOGO request while in state Ready
  kernel: host0: rport fffce5: Delete port
  kernel: host0: rport fffce5: Received PLOGI request
  kernel: host0: rport fffce5: Received PLOGI in state Delete - send busy
  kernel: host0: rport fffce5: work event 3
  kernel: host0: rport fffce5: lld callback ev 3
  kernel: host0: rport fffce5: work delete

Link: https://lore.kernel.org/r/20200626094959.32151-1-jhasan@marvell.comReviewed-by: Girish Basrur <gbasrur@marvell.com>
Reviewed-by: Saurav Kashyap <skashyap@marvell.com>
Reviewed-by: Shyam Sundar <ssundar@marvell.com>
Signed-off-by: Javed Hasan <jhasan@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libfc/fc_rport.c

@@ -483,10 +483,11 @@ static void fc_rport_enter_delete(struct fc_rport_priv *rdata,
 
 	fc_rport_state_enter(rdata, RPORT_ST_DELETE);
 
+	if (rdata->event == RPORT_EV_NONE) {
 		kref_get(&rdata->kref);
-	if (rdata->event == RPORT_EV_NONE &&
-	    !queue_work(rport_event_queue, &rdata->event_work))
+		if (!queue_work(rport_event_queue, &rdata->event_work))
 			kref_put(&rdata->kref, fc_rport_destroy);
+	}
 
 	rdata->event = event;
 }