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 <[email protected]>
---
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);
--
2.27.0
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 <[email protected]>
> ---
> 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 <[email protected]>
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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