[Intel-wired-lan] [PATCH] igb: Fix watchdog_task race with shutdown

[Ian Ray]

A rare [1] race condition is observed between the igb_watchdog_task and
shutdown on a dual-core i.MX6 based system with two I210 controllers.

Using printk, the igb_watchdog_task is hung in igb_read_phy_reg because
__igb_shutdown has already called __igb_close.

Fix this by locking in igb_watchdog_task (in the same way as is done in
igb_reset_task).

reboot             kworker

__igb_shutdown
  rtnl_lock
  __igb_close
  :                igb_watchdog_task
  :                :
  :                igb_read_phy_reg (hung)
  rtnl_unlock

[1] Note that this is easier to reproduce with 'initcall_debug' logging
and additional and printk logging in igb_main.

Signed-off-by: Ian Ray <ian....@gehealthcare.com>
---
 drivers/net/ethernet/intel/igb/igb_main.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c 
b/drivers/net/ethernet/intel/igb/igb_main.c
index c646c71915f0..a4910e565a3f 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -5544,6 +5544,8 @@ static void igb_watchdog_task(struct work_struct *work)
        u32 connsw;
        u16 phy_data, retry_count = 20;
 
+       rtnl_lock();
+
        link = igb_has_link(adapter);
 
        if (adapter->flags & IGB_FLAG_NEED_LINK_UPDATE) {
@@ -5680,7 +5682,7 @@ static void igb_watchdog_task(struct work_struct *work)
                                if (adapter->flags & IGB_FLAG_MEDIA_RESET) {
                                        schedule_work(&adapter->reset_task);
                                        /* return immediately */
-                                       return;
+                                       goto unlock;
                                }
                        }
                        pm_schedule_suspend(netdev->dev.parent,
@@ -5693,7 +5695,7 @@ static void igb_watchdog_task(struct work_struct *work)
                        if (adapter->flags & IGB_FLAG_MEDIA_RESET) {
                                schedule_work(&adapter->reset_task);
                                /* return immediately */
-                               return;
+                               goto unlock;
                        }
                }
        }
@@ -5714,7 +5716,7 @@ static void igb_watchdog_task(struct work_struct *work)
                                adapter->tx_timeout_count++;
                                schedule_work(&adapter->reset_task);
                                /* return immediately since reset is imminent */
-                               return;
+                               goto unlock;
                        }
                }
 
@@ -5751,6 +5753,9 @@ static void igb_watchdog_task(struct work_struct *work)
                        mod_timer(&adapter->watchdog_timer,
                                  round_jiffies(jiffies + 2 * HZ));
        }
+
+unlock:
+       rtnl_unlock();
 }
 
 enum latency_range {
-- 
2.49.0