[net] net: lapbether: Remove netif_start_queue / netif_stop_queue

For the devices in this driver, the default qdisc is "noqueue",
because their "tx_queue_len" is 0.

In function "__dev_queue_xmit" in "net/core/dev.c", devices with the
"noqueue" qdisc are specially handled. Packets are transmitted without
being queued after a "dev->flags & IFF_UP" check. However, it's possible
that even if this check succeeds, "ops->ndo_stop" may still have already
been called. This is because in "__dev_close_many", "ops->ndo_stop" is
called before clearing the "IFF_UP" flag.

If we call "netif_stop_queue" in "ops->ndo_stop", then it's possible in
"__dev_queue_xmit", it sees the "IFF_UP" flag is present, and then it
checks "netif_xmit_stopped" and finds that the queue is already stopped.
In this case, it will complain that:
"Virtual device ... asks to queue packet!"

To prevent "__dev_queue_xmit" from generating this complaint, we should
not call "netif_stop_queue" in "ops->ndo_stop".

We also don't need to call "netif_start_queue" in "ops->ndo_open",
because after a netdev is allocated and registered, the
"__QUEUE_STATE_DRV_XOFF" flag is initially not set, so there is no need
to call "netif_start_queue" to clear it.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/lapbether.c | 3 ---
 1 file changed, 3 deletions(-)

On 2021-03-07 12:33, Xie He wrote:
> For the devices in this driver, the default qdisc is "noqueue",

> because their "tx_queue_len" is 0.

> 

> In function "__dev_queue_xmit" in "net/core/dev.c", devices with the

> "noqueue" qdisc are specially handled. Packets are transmitted without

> being queued after a "dev->flags & IFF_UP" check. However, it's 

> possible

> that even if this check succeeds, "ops->ndo_stop" may still have 

> already

> been called. This is because in "__dev_close_many", "ops->ndo_stop" is

> called before clearing the "IFF_UP" flag.

> 

> If we call "netif_stop_queue" in "ops->ndo_stop", then it's possible in

> "__dev_queue_xmit", it sees the "IFF_UP" flag is present, and then it

> checks "netif_xmit_stopped" and finds that the queue is already 

> stopped.

> In this case, it will complain that:

> "Virtual device ... asks to queue packet!"

> 

> To prevent "__dev_queue_xmit" from generating this complaint, we should

> not call "netif_stop_queue" in "ops->ndo_stop".

> 

> We also don't need to call "netif_start_queue" in "ops->ndo_open",

> because after a netdev is allocated and registered, the

> "__QUEUE_STATE_DRV_XOFF" flag is initially not set, so there is no need

> to call "netif_start_queue" to clear it.

> 

> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

> Signed-off-by: Xie He <xie.he.0141@gmail.com>

> ---

>  drivers/net/wan/lapbether.c | 3 ---

>  1 file changed, 3 deletions(-)

> 

> diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c

> index 605fe555e157..c3372498f4f1 100644

> --- a/drivers/net/wan/lapbether.c

> +++ b/drivers/net/wan/lapbether.c

> @@ -292,7 +292,6 @@ static int lapbeth_open(struct net_device *dev)

>  		return -ENODEV;

>  	}

> 

> -	netif_start_queue(dev);

>  	return 0;

>  }

> 

> @@ -300,8 +299,6 @@ static int lapbeth_close(struct net_device *dev)

>  {

>  	int err;

> 

> -	netif_stop_queue(dev);

> -

>  	if ((err = lapb_unregister(dev)) != LAPB_OK)

>  		pr_err("lapb_unregister error: %d\n", err);


Seems reasonable to me.

Acked-by: Martin Schiller <ms@dev.tdt.de>

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Sun,  7 Mar 2021 03:33:07 -0800 you wrote:
> For the devices in this driver, the default qdisc is "noqueue",

> because their "tx_queue_len" is 0.

> 

> In function "__dev_queue_xmit" in "net/core/dev.c", devices with the

> "noqueue" qdisc are specially handled. Packets are transmitted without

> being queued after a "dev->flags & IFF_UP" check. However, it's possible

> that even if this check succeeds, "ops->ndo_stop" may still have already

> been called. This is because in "__dev_close_many", "ops->ndo_stop" is

> called before clearing the "IFF_UP" flag.

> 

> [...]


Here is the summary with links:
  - [net] net: lapbether: Remove netif_start_queue / netif_stop_queue
    https://git.kernel.org/netdev/net/c/f7d9d4854519

You are awesome, thank you!
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