e1000e: Fix link check race condition

Alex reported the following race condition:

/* link goes up... interrupt... schedule watchdog */
\ e1000_watchdog_task
	\ e1000e_has_link
		\ hw->mac.ops.check_for_link() === e1000e_check_for_copper_link
			\ e1000e_phy_has_link_generic(..., &link)
				link = true

					 /* link goes down... interrupt */
					 \ e1000_msix_other
						 hw->mac.get_link_status = true

			/* link is up */
			mac->get_link_status = false

		link_active = true
		/* link_active is true, wrongly, and stays so because
		 * get_link_status is false */

Avoid this problem by making sure that we don't set get_link_status = false
after having checked the link.

It seems this problem has been present since the introduction of e1000e.

Link: https://lkml.org/lkml/2018/1/29/338
Reported-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/ich8lan.c

@@ -1383,19 +1383,20 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 	 */
 	if (!mac->get_link_status)
 		return 0;
+	mac->get_link_status = false;
 
 	/* First we want to see if the MII Status Register reports
 	 * link.  If so, then we want to get the current speed/duplex
 	 * of the PHY.
 	 */
 	ret_val = e1000e_phy_has_link_generic(hw, 1, 0, &link);
 	if (ret_val)
-		return ret_val;
+		goto out;
 
 	if (hw->mac.type == e1000_pchlan) {
 		ret_val = e1000_k1_gig_workaround_hv(hw, link);
 		if (ret_val)
-			return ret_val;
+			goto out;
 	}
 
 	/* When connected at 10Mbps half-duplex, some parts are excessively
@@ -1428,7 +1429,7 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 
 		ret_val = hw->phy.ops.acquire(hw);
 		if (ret_val)
-			return ret_val;
+			goto out;
 
 		if (hw->mac.type == e1000_pch2lan)
 			emi_addr = I82579_RX_CONFIG;
@@ -1450,7 +1451,7 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 		hw->phy.ops.release(hw);
 
 		if (ret_val)
-			return ret_val;
+			goto out;
 
 		if (hw->mac.type >= e1000_pch_spt) {
 			u16 data;
@@ -1459,14 +1460,14 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 			if (speed == SPEED_1000) {
 				ret_val = hw->phy.ops.acquire(hw);
 				if (ret_val)
-					return ret_val;
+					goto out;
 
 				ret_val = e1e_rphy_locked(hw,
 							  PHY_REG(776, 20),
 							  &data);
 				if (ret_val) {
 					hw->phy.ops.release(hw);
-					return ret_val;
+					goto out;
 				}
 
 				ptr_gap = (data & (0x3FF << 2)) >> 2;
@@ -1480,18 +1481,18 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 				}
 				hw->phy.ops.release(hw);
 				if (ret_val)
-					return ret_val;
+					goto out;
 			} else {
 				ret_val = hw->phy.ops.acquire(hw);
 				if (ret_val)
-					return ret_val;
+					goto out;
 
 				ret_val = e1e_wphy_locked(hw,
 							  PHY_REG(776, 20),
 							  0xC023);
 				hw->phy.ops.release(hw);
 				if (ret_val)
-					return ret_val;
+					goto out;
 
 			}
 		}
@@ -1518,15 +1519,15 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 	    (hw->adapter->pdev->device == E1000_DEV_ID_PCH_I218_V3)) {
 		ret_val = e1000_k1_workaround_lpt_lp(hw, link);
 		if (ret_val)
-			return ret_val;
+			goto out;
 	}
 	if (hw->mac.type >= e1000_pch_lpt) {
 		/* Set platform power management values for
 		 * Latency Tolerance Reporting (LTR)
 		 */
 		ret_val = e1000_platform_pm_pch_lpt(hw, link);
 		if (ret_val)
-			return ret_val;
+			goto out;
 	}
 
 	/* Clear link partner's EEE ability */
@@ -1549,9 +1550,7 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 	}
 
 	if (!link)
-		return 0;	/* No link detected */
-
-	mac->get_link_status = false;
+		goto out;
 
 	switch (hw->mac.type) {
 	case e1000_pch2lan:
@@ -1617,6 +1616,10 @@ static s32 e1000_check_for_copper_link_ich8lan(struct e1000_hw *hw)
 		e_dbg("Error configuring flow control\n");
 
 	return ret_val;
+
+out:
+	mac->get_link_status = true;
+	return ret_val;
 }
 
 static s32 e1000_get_variants_ich8lan(struct e1000_adapter *adapter)

drivers/net/ethernet/intel/e1000e/mac.c

@@ -424,19 +424,15 @@ s32 e1000e_check_for_copper_link(struct e1000_hw *hw)
 	 */
 	if (!mac->get_link_status)
 		return 0;
+	mac->get_link_status = false;
 
 	/* First we want to see if the MII Status Register reports
 	 * link.  If so, then we want to get the current speed/duplex
 	 * of the PHY.
 	 */
 	ret_val = e1000e_phy_has_link_generic(hw, 1, 0, &link);
-	if (ret_val)
-		return ret_val;
-
-	if (!link)
-		return 0;	/* No link detected */
-
-	mac->get_link_status = false;
+	if (ret_val || !link)
+		goto out;
 
 	/* Check if there was DownShift, must be checked
 	 * immediately after link-up
@@ -465,6 +461,10 @@ s32 e1000e_check_for_copper_link(struct e1000_hw *hw)
 		e_dbg("Error configuring flow control\n");
 
 	return ret_val;
+
+out:
+	mac->get_link_status = true;
+	return ret_val;
 }
 
 /**