[PATCH net] i40e: fix memcmp of pointer in i40e_hw_set_dcb_config()

[Aaron Esau <aaron1esau@gmail.com>]

In i40e_hw_set_dcb_config(), both new_cfg and old_cfg are pointers to
struct i40e_dcbx_config, so sizeof(new_cfg) evaluates to the size of a
pointer (8 bytes on 64-bit) rather than the size of the struct. Likewise,
&new_cfg and &old_cfg are the addresses of the pointer variables on the
stack, not the addresses of the actual config structs.

As a result, the memcmp never compares the actual configuration data,
meaning the "no change needed" early return never fires. Every call to
this function performs a full DCB reconfiguration (quiescing all VSIs,
reprogramming via "Set LLDP MIB" AQC, and reconfiguring VEB/VSIs) even
when the configuration has not changed.

Fix this by comparing the structs themselves rather than the pointers.

Fixes: 4b208eaa8078 ("i40e: Add init and default config of software based DCB")
Cc: stable@vger.kernel.org
Signed-off-by: Aaron Esau <aaron1esau@gmail.com>
---

Found using Coccinelle/spatch with a semantic patch that matches
sizeof(ptr) and &ptr used together where ptr is a pointer type.

 drivers/net/ethernet/intel/i40e/i40e_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index XXXXXXX..XXXXXXX 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
@@ -6904,7 +6904,7 @@ static int i40e_hw_set_dcb_config(struct i40e_pf *pf,
 	int ret;

 	/* Check if need reconfiguration */
-	if (!memcmp(&new_cfg, &old_cfg, sizeof(new_cfg))) {
+	if (!memcmp(new_cfg, old_cfg, sizeof(*new_cfg))) {
 		dev_dbg(&pf->pdev->dev, "No Change in DCB Config required.\n");
 		return 0;
 	}
--
2.49.0