[PATCH net] net: rollback orig value on failure of dev_qdisc_change_tx_queue_len

[PATCH net] net: rollback orig value on failure of dev_qdisc_change_tx_queue_len

[Tariq Toukan]

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.

The revert of changes in dev_qdisc_change_tx_queue_len
in such case is needed but missing (marked as TODO), yet it is
still better to not apply the new requested value.

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

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

Re: [PATCH net] net: rollback orig value on failure of dev_qdisc_change_tx_queue_len

[Cong Wang]

On Thu, Jul 19, 2018 at 7:34 AM Tariq Toukan <tariqt@mellanox.com> wrote:
>
> 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.
>
> The revert of changes in dev_qdisc_change_tx_queue_len
> in such case is needed but missing (marked as TODO), yet it is
> still better to not apply the new requested value.

You misunderstand the TODO, that is for reverting tx queue len
change for previous queues in the loop. I still don't have any
nice solution for this yet.

Yeah, your change itself looks good.

Please update the changelog.

Thanks.

Re: [PATCH net] net: rollback orig value on failure of dev_qdisc_change_tx_queue_len

[Tariq Toukan]

On 19/07/2018 8:25 PM, Cong Wang wrote:
> On Thu, Jul 19, 2018 at 7:34 AM Tariq Toukan <tariqt@mellanox.com> wrote:
>>
>> 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.
>>
>> The revert of changes in dev_qdisc_change_tx_queue_len
>> in such case is needed but missing (marked as TODO), yet it is
>> still better to not apply the new requested value.
> 
> You misunderstand the TODO, that is for reverting tx queue len
> change for previous queues in the loop. I still don't have any
> nice solution for this yet.
> 
I understood this, but maybe didn't describe it clearly. I'll re-phrase.

> Yeah, your change itself looks good.
> 

Thanks.

> Please update the changelog.
> 
> Thanks.
>