netdev - [PATCH net] net: lapbether: Remove netif_start_queue / netif_stop

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Date:   Sun,  7 Mar 2021 03:33:07 -0800
From:   Xie He <xie.he.0141@...il.com>
To:     Martin Schiller <ms@....tdt.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Xie He <xie.he.0141@...il.com>
Subject: [PATCH 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@...il.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);

-- 
2.27.0