bnxt_en: Fix possible crash in bnxt_fw_reset_task().

bnxt_fw_reset_task() is run from a delayed workqueue.  The current
code is not cancelling the workqueue in the driver's .remove()
method and it can potentially crash if the device is removed with
the workqueue still pending.

The fix is to clear the BNXT_STATE_IN_FW_RESET flag and then cancel
the delayed workqueue in bnxt_remove_one().  bnxt_queue_fw_reset_work()
also needs to check that this flag is set before scheduling.  This
will guarantee that no rescheduling will be done after it is cancelled.

Fixes: 230d1f0d ("bnxt_en: Handle firmware reset.")
Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -1141,6 +1141,9 @@ static int bnxt_discard_rx(struct bnxt *bp, struct bnxt_cp_ring_info *cpr,
 
 static void bnxt_queue_fw_reset_work(struct bnxt *bp, unsigned long delay)
 {
+	if (!(test_bit(BNXT_STATE_IN_FW_RESET, &bp->state)))
+		return;
+
 	if (BNXT_PF(bp))
 		queue_delayed_work(bnxt_pf_wq, &bp->fw_reset_task, delay);
 	else
@@ -1157,10 +1160,12 @@ static void bnxt_queue_sp_work(struct bnxt *bp)
 
 static void bnxt_cancel_sp_work(struct bnxt *bp)
 {
-	if (BNXT_PF(bp))
+	if (BNXT_PF(bp)) {
 		flush_workqueue(bnxt_pf_wq);
-	else
+	} else {
 		cancel_work_sync(&bp->sp_task);
+		cancel_delayed_work_sync(&bp->fw_reset_task);
+	}
 }
 
 static void bnxt_sched_reset(struct bnxt *bp, struct bnxt_rx_ring_info *rxr)
@@ -11761,6 +11766,7 @@ static void bnxt_remove_one(struct pci_dev *pdev)
 	unregister_netdev(dev);
 	bnxt_dl_unregister(bp);
 	bnxt_shutdown_tc(bp);
+	clear_bit(BNXT_STATE_IN_FW_RESET, &bp->state);
 	bnxt_cancel_sp_work(bp);
 	bp->sp_event = 0;