netdev - [PATCH net v2] net: rollback orig value on failure of dev_qdisc_change_tx_queue

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Date:   Tue, 24 Jul 2018 14:12:20 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Eran Ben Elisha <eranbe@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: [PATCH net v2] net: rollback orig value on failure of dev_qdisc_change_tx_queue_len

Fix dev_change_tx_queue_len so it rolls back original value
upon a failure in dev_qdisc_change_tx_queue_len.
This is already done for notifirers' failures, share the code.

In case of failure in dev_qdisc_change_tx_queue_len, some tx queues
would still be of the new length, while they should be reverted.
Currently, the revert is not done, and is marked with a TODO label
in dev_qdisc_change_tx_queue_len, and should find some nice solution
to do it.
Yet it is still better to not apply the newly requested value.

Fixes: 48bfd55e7e41 ("net_sched: plug in qdisc ops change_tx_queue_len")
Signed-off-by: Tariq Toukan <tariqt@...lanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@...lanox.com>
Reported-by: Ran Rozenstein <ranro@...lanox.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
---
 net/core/dev.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

v1 -> v2:
* Updated commit message, per Cong's comment.

diff --git a/net/core/dev.c b/net/core/dev.c
index a5aa1c7444e6..559a91271f82 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7149,16 +7149,19 @@ int dev_change_tx_queue_len(struct net_device *dev, unsigned long new_len)
 		dev->tx_queue_len = new_len;
 		res = call_netdevice_notifiers(NETDEV_CHANGE_TX_QUEUE_LEN, dev);
 		res = notifier_to_errno(res);
-		if (res) {
-			netdev_err(dev,
-				   "refused to change device tx_queue_len\n");
-			dev->tx_queue_len = orig_len;
-			return res;
-		}
-		return dev_qdisc_change_tx_queue_len(dev);
+		if (res)
+			goto err_rollback;
+		res = dev_qdisc_change_tx_queue_len(dev);
+		if (res)
+			goto err_rollback;
 	}
 
 	return 0;
+
+err_rollback:
+	netdev_err(dev, "refused to change device tx_queue_len\n");
+	dev->tx_queue_len = orig_len;
+	return res;
 }
 
 /**
-- 
1.8.3.1