[PATCH v1 1/3] mlxbf_gige: Fix kernel panic at shutdown

There is a race condition happening during shutdown due to pending napi transactions.
Since mlxbf_gige_poll is still running, it tries to access a NULL pointer and as a
result causes a kernel panic:

[  284.074822] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000070
...
[  284.322326] Call trace:
[  284.324757]  mlxbf_gige_handle_tx_complete+0xc8/0x170 [mlxbf_gige]
[  284.330924]  mlxbf_gige_poll+0x54/0x160 [mlxbf_gige]
[  284.335876]  __napi_poll+0x40/0x1c8
[  284.339353]  net_rx_action+0x314/0x3a0
[  284.343086]  __do_softirq+0x128/0x334
[  284.346734]  run_ksoftirqd+0x54/0x6c
[  284.350294]  smpboot_thread_fn+0x14c/0x190
[  284.354375]  kthread+0x10c/0x110
[  284.357588]  ret_from_fork+0x10/0x20
[  284.361150] Code: 8b070000 f9000ea0 f95056c0 f86178a1 (b9407002)
[  284.367227] ---[ end trace a18340bbb9ea2fa7 ]---

To fix this, return in the case where "priv" is NULL.

Fixes: f92e1869d74e ("Add Mellanox BlueField Gigabit Ethernet driver")
Signed-off-by: Asmaa Mnebhi <asmaa@nvidia.com>
Reviewed-by: David Thompson <davthompson@nvidia.com>
---
 drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c b/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c
index 0d5a41a2ae01..cfb8fb957f0c 100644
--- a/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c
+++ b/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c

@@ -298,6 +298,9 @@ int mlxbf_gige_poll(struct napi_struct *napi, int budget)
 
 	priv = container_of(napi, struct mlxbf_gige, napi);
 
+	if (!priv)
+		return 0;
+
 	mlxbf_gige_handle_tx_complete(priv);
 
 	do {

-- 
2.30.1