cxgb4: avoid crash on PCI error recovery path

During PCI error recovery process, specifically on eeh_err_detected()
we might have a NULL netdev struct, hence a direct dereference will
lead to a kernel oops. This was observed with latest upstream kernel
(v4.12-rc2) on Chelsio adapter T422-CR in PowerPC machines.

This patch checks for NULL pointer and avoids the crash, both in
eeh_err_detected() and eeh_resume(). Also, we avoid to trigger
a fatal error or to try disabling interrupts on FW during PCI
error recovery, because: (a) driver might not be able to accurately
access PCI regions in this case, and (b) trigger a fatal error
_during_ the recovery steps is a mistake that could prevent the
recovery path to complete successfully.
Reported-by: Harsha Thyagaraja <hathyaga@in.ibm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c

@@ -2771,6 +2771,9 @@ void t4_fatal_err(struct adapter *adap)
 {
 	int port;
 
+	if (pci_channel_offline(adap->pdev))
+		return;
+
 	/* Disable the SGE since ULDs are going to free resources that
 	 * could be exposed to the adapter.  RDMA MWs for example...
 	 */
@@ -3882,9 +3885,10 @@ static pci_ers_result_t eeh_err_detected(struct pci_dev *pdev,
 	spin_lock(&adap->stats_lock);
 	for_each_port(adap, i) {
 		struct net_device *dev = adap->port[i];
-
-		netif_device_detach(dev);
-		netif_carrier_off(dev);
+		if (dev) {
+			netif_device_detach(dev);
+			netif_carrier_off(dev);
+		}
 	}
 	spin_unlock(&adap->stats_lock);
 	disable_interrupts(adap);
@@ -3963,12 +3967,13 @@ static void eeh_resume(struct pci_dev *pdev)
 	rtnl_lock();
 	for_each_port(adap, i) {
 		struct net_device *dev = adap->port[i];
-
-		if (netif_running(dev)) {
-			link_start(dev);
-			cxgb_set_rxmode(dev);
+		if (dev) {
+			if (netif_running(dev)) {
+				link_start(dev);
+				cxgb_set_rxmode(dev);
+			}
+			netif_device_attach(dev);
 		}
-		netif_device_attach(dev);
 	}
 	rtnl_unlock();
 }

drivers/net/ethernet/chelsio/cxgb4/t4_hw.c

@@ -4557,8 +4557,13 @@ void t4_intr_enable(struct adapter *adapter)
  */
 void t4_intr_disable(struct adapter *adapter)
 {
-	u32 whoami = t4_read_reg(adapter, PL_WHOAMI_A);
-	u32 pf = CHELSIO_CHIP_VERSION(adapter->params.chip) <= CHELSIO_T5 ?
+	u32 whoami, pf;
+
+	if (pci_channel_offline(adapter->pdev))
+		return;
+
+	whoami = t4_read_reg(adapter, PL_WHOAMI_A);
+	pf = CHELSIO_CHIP_VERSION(adapter->params.chip) <= CHELSIO_T5 ?
 			SOURCEPF_G(whoami) : T6_SOURCEPF_G(whoami);
 
 	t4_write_reg(adapter, MYPF_REG(PL_PF_INT_ENABLE_A), 0);