[PATCH v2] 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.

The fix is to delete timer and cancel the work after settting IGB_DOWN.
This approach mirrors igb_up.

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.ray@xxxxxxxxxxxxxxxx>
---
Changes in v2:
- Change strategy to avoid taking RTNL.
- Link to v1: https://lore.kernel.org/all/20250428115450.639-1-ian.ray@xxxxxxxxxxxxxxxx/
---
 drivers/net/ethernet/intel/igb/igb_main.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index 9e9a5900e6e5..a65ae7925ae8 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -2175,10 +2175,14 @@ void igb_down(struct igb_adapter *adapter)
 	u32 tctl, rctl;
 	int i;

-	/* signal that we're down so the interrupt handler does not
-	 * reschedule our watchdog timer
+	/* The watchdog timer may be rescheduled, so explicitly
+	 * disable watchdog from being rescheduled.
 	 */
 	set_bit(__IGB_DOWN, &adapter->state);
+	timer_delete_sync(&adapter->watchdog_timer);
+	timer_delete_sync(&adapter->phy_info_timer);
+
+	cancel_work_sync(&adapter->watchdog_task);

 	/* disable receives in the hardware */
 	rctl = rd32(E1000_RCTL);
@@ -2210,9 +2214,6 @@ void igb_down(struct igb_adapter *adapter)
 		}
 	}

-	timer_delete_sync(&adapter->watchdog_timer);
-	timer_delete_sync(&adapter->phy_info_timer);
-
 	/* record the stats before reset*/
 	spin_lock(&adapter->stats64_lock);
 	igb_update_stats(adapter);
--
2.49.0