[PATCH 4.9 41/66] net: caif: remove BUG_ON(dev == NULL) in caif_xmit

Greg Kroah-Hartman
2021-05-31T13:33:25Z

From: Du Cheng <ducheng2@gmail.com>

[ Upstream commit 65a67792e3416f7c5d7daa47d99334cbb19a7449 ]

The condition of dev == NULL is impossible in caif_xmit(), hence it is
for the removal.

Explanation:
The static caif_xmit() is only called upon via a function pointer
`ndo_start_xmit` defined in include/linux/netdevice.h:
```
struct net_device_ops {
...
netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb, struct net_device *dev);
...
}
```

The exhausive list of call points are:
```
drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
dev->netdev_ops->ndo_start_xmit(skb, dev);
^ ^

drivers/infiniband/ulp/opa_vnic/opa_vnic_netdev.c
struct opa_vnic_adapter *adapter = opa_vnic_priv(netdev);
^ ^
return adapter->rn_ops->ndo_start_xmit(skb, netdev); // adapter would crash first
^ ^

drivers/usb/gadget/function/f_ncm.c
ncm->netdev->netdev_ops->ndo_start_xmit(NULL, ncm->netdev);
^ ^

include/linux/netdevice.h
static inline netdev_tx_t __netdev_start_xmit(...
{
return ops->ndo_start_xmit(skb, dev);
^
}

const struct net_device_ops *ops = dev->netdev_ops;
^
rc = __netdev_start_xmit(ops, skb, dev, more);
^
```

In each of the enumerated scenarios, it is impossible for the NULL-valued dev to
reach the caif_xmit() without crashing the kernel earlier, therefore `BUG_ON(dev ==
NULL)` is rather useless, hence the removal.

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Du Cheng <ducheng2@gmail.com>
Link: https://lore.kernel.org/r/20210503115736.2104747-20-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/caif/caif_serial.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c
index c2dea4916e5d..32834dad0b83 100644
--- a/drivers/net/caif/caif_serial.c
+++ b/drivers/net/caif/caif_serial.c
@@ -281,7 +281,6 @@ static int caif_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct ser_device *ser;

- BUG_ON(dev == NULL);
ser = netdev_priv(dev);

/* Send flow off once, on high water mark */
--
2.30.2