[PATCH iwl-net] e1000: Move cancel_work_sync to avoid deadlock

[Joe Damato <jdamato@fastly.com>]

Previously, e1000_down called cancel_work_sync for the e1000 reset task
(via e1000_down_and_stop), which takes RTNL.

As reported by users and syzbot, a deadlock is possible due to lock
inversion in the following scenario:

CPU 0:
  - RTNL is held
  - e1000_close
  - e1000_down
  - cancel_work_sync (takes the work queue mutex)
  - e1000_reset_task

CPU 1:
  - process_one_work (takes the work queue mutex)
  - e1000_reset_task (takes RTNL)

To remedy this, avoid calling cancel_work_sync from e1000_down
(e1000_reset_task does nothing if the device is down anyway). Instead,
call cancel_work_sync for e1000_reset_task when the device is being
removed.

Fixes: e400c7444d84 ("e1000: Hold RTNL when e1000_down can be called")
Reported-by: syzbot+846bb38dc67fe62cc733@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/683837bf.a00a0220.52848.0003.GAE@google.com/
Reported-by: John <john.cs.hey@gmail.com>
Closes: https://lore.kernel.org/netdev/CAP=Rh=OEsn4y_2LvkO3UtDWurKcGPnZ_NPSXK=FbgygNXL37Sw@mail.gmail.com/
Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 drivers/net/ethernet/intel/e1000/e1000_main.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
index 3f089c3d47b2..d8595e84326d 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -477,10 +477,6 @@ static void e1000_down_and_stop(struct e1000_adapter *adapter)
 
 	cancel_delayed_work_sync(&adapter->phy_info_task);
 	cancel_delayed_work_sync(&adapter->fifo_stall_task);
-
-	/* Only kill reset task if adapter is not resetting */
-	if (!test_bit(__E1000_RESETTING, &adapter->flags))
-		cancel_work_sync(&adapter->reset_task);
 }
 
 void e1000_down(struct e1000_adapter *adapter)
@@ -1266,6 +1262,10 @@ static void e1000_remove(struct pci_dev *pdev)
 
 	unregister_netdev(netdev);
 
+	/* Only kill reset task if adapter is not resetting */
+	if (!test_bit(__E1000_RESETTING, &adapter->flags))
+		cancel_work_sync(&adapter->reset_task);
+
 	e1000_phy_hw_reset(hw);
 
 	kfree(adapter->tx_ring);
-- 
2.43.0