[PATCH 4.9 24/83] e1000: fix race condition between e1000_down() and e1000_watchdog

Greg Kroah-Hartman
2018-11-19T16:53:17Z

[ Upstream commit 44c445c3d1b4eacff23141fa7977c3b2ec3a45c9 ]

This patch fixes a race condition that can result into the interface being
up and carrier on, but with transmits disabled in the hardware.
The bug may show up by repeatedly IFF_DOWN+IFF_UP the interface, which
allows e1000_watchdog() interleave with e1000_down().

CPU x CPU y
--------------------------------------------------------------------
e1000_down():
netif_carrier_off()
e1000_watchdog():
if (carrier == off) {
netif_carrier_on();
enable_hw_transmit();
}
disable_hw_transmit();
e1000_watchdog():
/* carrier on, do nothing */

Signed-off-by: Vincenzo Maffione <v.maffione@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/intel/e1000/e1000_main.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
index dd112aa5cebb..39a09e18c1b7 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -521,8 +521,6 @@ void e1000_down(struct e1000_adapter *adapter)
struct net_device *netdev = adapter->netdev;
u32 rctl, tctl;

- netif_carrier_off(netdev);
-
/* disable receives in the hardware */
rctl = er32(RCTL);
ew32(RCTL, rctl & ~E1000_RCTL_EN);
@@ -538,6 +536,15 @@ void e1000_down(struct e1000_adapter *adapter)
E1000_WRITE_FLUSH();
msleep(10);

+ /* Set the carrier off after transmits have been disabled in the
+ * hardware, to avoid race conditions with e1000_watchdog() (which
+ * may be running concurrently to us, checking for the carrier
+ * bit to decide whether it should enable transmits again). Such
+ * a race condition would result into transmission being disabled
+ * in the hardware until the next IFF_DOWN+IFF_UP cycle.
+ */
+ netif_carrier_off(netdev);
+
napi_disable(&adapter->napi);

e1000_irq_disable(adapter);
--
2.17.1