linux-kernel - [PATCH 4.4 043/342] IFF_NO_QUEUE: Fix for drivers not calling ether

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Date:	Tue, 01 Mar 2016 23:53:57 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Phil Sutter <phil@....cc>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 043/342] IFF_NO_QUEUE: Fix for drivers not calling ether_setup()

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Phil Sutter <phil@....cc>

[ Upstream commit a813104d923339144078939175faf4e66aca19b4 ]

My implementation around IFF_NO_QUEUE driver flag assumed that leaving
tx_queue_len untouched (specifically: not setting it to zero) by drivers
would make it possible to assign a regular qdisc to them without having
to worry about setting tx_queue_len to a useful value. This was only
partially true: I overlooked that some drivers don't call ether_setup()
and therefore not initialize tx_queue_len to the default value of 1000.
Consequently, removing the workarounds in place for that case in qdisc
implementations which cared about it (namely, pfifo, bfifo, gred, htb,
plug and sfb) leads to problems with these specific interface types and
qdiscs.

Luckily, there's already a sanitization point for drivers setting
tx_queue_len to zero, which can be reused to assign the fallback value
most qdisc implementations used, which is 1.

Fixes: 348e3435cbefa ("net: sched: drop all special handling of tx_queue_len == 0")
Tested-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Phil Sutter <phil@....cc>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/dev.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7128,8 +7128,10 @@ struct net_device *alloc_netdev_mqs(int
 	dev->priv_flags = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
 	setup(dev);

-	if (!dev->tx_queue_len)
+	if (!dev->tx_queue_len) {
 		dev->priv_flags |= IFF_NO_QUEUE;
+		dev->tx_queue_len = 1;
+	}

 	dev->num_tx_queues = txqs;
 	dev->real_num_tx_queues = txqs;