[RFC iwl-net] e1000: Hold RTNL when e1000_down can be called

[Joe Damato <jdamato@fastly.com>]

e1000_down calls netif_queue_set_napi, which assumes that RTNL is held.

There are a few paths for e1000_down to be called in e1000 where RTNL is
not currently being held:
  - e1000_shutdown (pci shutdown)
  - e1000_suspend (power management)
  - e1000_reinit_locked (via e1000_reset_task delayed work)

Hold RTNL in two places to fix this issue:
  - e1000_reset_task
  - __e1000_shutdown (which is called from both e1000_shutdown and
    e1000_suspend).

The other paths which call e1000_down seemingly hold RTNL and are OK:
  - e1000_close (ndo_stop)
  - e1000_change_mtu (ndo_change_mtu)

I'm submitting this is as an RFC because:
  - the e1000_reinit_locked issue appears very similar to commit
    21f857f0321d ("e1000e: add rtnl_lock() to e1000_reset_task"), which
    fixes a similar issue in e1000e

however

  - adding rtnl to e1000_reinit_locked seemingly conflicts with an
    earlier e1000 commit b2f963bfaeba ("e1000: fix lockdep warning in
    e1000_reset_task").

Hopefully Intel can weigh in and shed some light on the correct way to
go.

Fixes: 8f7ff18a5ec7 ("e1000: Link NAPI instances to queues and IRQs")
Reported-by: Dmitry Antipov <dmantipov@yandex.ru>
Closes: https://lore.kernel.org/netdev/8cf62307-1965-46a0-a411-ff0080090ff9@yandex.ru/
Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 drivers/net/ethernet/intel/e1000/e1000_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
index 4de9b156b2be..9ed99c75d59e 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -3509,7 +3509,9 @@ static void e1000_reset_task(struct work_struct *work)
 		container_of(work, struct e1000_adapter, reset_task);
 
 	e_err(drv, "Reset adapter\n");
+	rtnl_lock();
 	e1000_reinit_locked(adapter);
+	rtnl_unlock();
 }
 
 /**
@@ -5074,7 +5076,9 @@ static int __e1000_shutdown(struct pci_dev *pdev, bool *enable_wake)
 			usleep_range(10000, 20000);
 
 		WARN_ON(test_bit(__E1000_RESETTING, &adapter->flags));
+		rtnl_lock();
 		e1000_down(adapter);
+		rtnl_unlock();
 	}
 
 	status = er32(STATUS);

base-commit: d811ac148f0afd2f3f7e1cd7f54de8da973ec5e3
-- 
2.25.1