[PATCH iwl-net] i40e: fix napi_disable hang in i40e_down() during firmware update

[mheib@redhat.com]

From: Mohammad Heib <mheib@redhat.com>

i40e_down() expects its caller to set __I40E_VSI_DOWN before calling it,
as noted in the comment at the top of the function. All callers do this
except i40e_vsi_reinit_locked(), which calls i40e_down() directly
without setting the flag.

Normally this doesn't cause problems because NAPI drains cleanly on its
own. But when the hardware is in a bad state, like during an NVM
firmware update, the ring descriptors can contain garbage that
i40e_napi_poll() sees as real work. Since __I40E_VSI_DOWN isn't set, the
poll function has no reason to bail out. It keeps returning budget,
napi_disable() keeps waiting, and the whole thing hangs. The thread
stuck in napi_disable() is usually NetworkManager, and because it holds
the RTNL lock, the system can end up completely frozen.

Set __I40E_VSI_DOWN in i40e_vsi_reinit_locked() before calling
i40e_down(). i40e_up_complete() already clears the flag when the VSI
comes back up, so no additional cleanup is needed.

Fixes: 41c445ff0f48 ("i40e: main driver core")
Signed-off-by: Mohammad Heib <mheib@redhat.com>
---
 drivers/net/ethernet/intel/i40e/i40e_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index 878e0c46e5bb..78f95f63b588 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
@@ -7463,6 +7463,8 @@ static void i40e_vsi_reinit_locked(struct i40e_vsi *vsi)
 
 	while (test_and_set_bit(__I40E_CONFIG_BUSY, pf->state))
 		usleep_range(1000, 2000);
+	/* required by i40e_down() */
+	set_bit(__I40E_VSI_DOWN, vsi->state);
 	i40e_down(vsi);
 
 	i40e_up(vsi);
-- 
2.53.0