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Date: Sat, 12 Oct 2019 20:42:09 +0900
From: Taehee Yoo <ap420073@...il.com>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: David Miller <davem@...emloft.net>,
Netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
Jakub Kicinski <jakub.kicinski@...ronome.com>,
Johannes Berg <johannes@...solutions.net>,
j.vosburgh@...il.com, vfalico@...il.com,
Andy Gospodarek <andy@...yhouse.net>,
Jiří Pírko <jiri@...nulli.us>,
Roopa Prabhu <roopa@...ulusnetworks.com>, saeedm@...lanox.com,
manishc@...vell.com, rahulv@...vell.com, kys@...rosoft.com,
haiyangz@...rosoft.com,
Stephen Hemminger <stephen@...workplumber.org>,
sashal@...nel.org, hare@...e.de, varun@...lsio.com,
ubraun@...ux.ibm.com, kgraul@...ux.ibm.com,
Jay Vosburgh <jay.vosburgh@...onical.com>,
Cody Schuffelen <schuffelen@...gle.com>, bjorn@...k.no
Subject: Re: [PATCH net v4 01/12] net: core: limit nested device depth
On Thu, 10 Oct 2019 at 19:19, Sabrina Dubroca <sd@...asysnail.net> wrote:
>
Hi Sabrina,
Thank you for review and testing!
> 2019-09-28, 16:48:32 +0000, Taehee Yoo wrote:
> > @@ -6790,23 +6878,45 @@ int netdev_walk_all_lower_dev(struct net_device *dev,
> > void *data),
> > void *data)
> > {
> > - struct net_device *ldev;
> > - struct list_head *iter;
> > - int ret;
> > + struct net_device *ldev, *next, *now, *dev_stack[MAX_NEST_DEV + 1];
> > + struct list_head *niter, *iter, *iter_stack[MAX_NEST_DEV + 1];
> > + int ret, cur = 0;
> >
> > - for (iter = &dev->adj_list.lower,
> > - ldev = netdev_next_lower_dev(dev, &iter);
> > - ldev;
> > - ldev = netdev_next_lower_dev(dev, &iter)) {
> > - /* first is the lower device itself */
> > - ret = fn(ldev, data);
> > - if (ret)
> > - return ret;
> > + now = dev;
> > + iter = &dev->adj_list.lower;
> >
> > - /* then look at all of its lower devices */
> > - ret = netdev_walk_all_lower_dev(ldev, fn, data);
> > - if (ret)
> > - return ret;
> > + while (1) {
> > + if (now != dev) {
> > + ret = fn(now, data);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + next = NULL;
> > + while (1) {
> > + ldev = netdev_next_lower_dev(now, &iter);
> > + if (!ldev)
> > + break;
> > +
> > + if (!next) {
> > + next = ldev;
> > + niter = &ldev->adj_list.lower;
> > + } else {
> > + dev_stack[cur] = ldev;
> > + iter_stack[cur++] = &ldev->adj_list.lower;
> > + break;
> > + }
> > + }
> > +
> > + if (!next) {
> > + if (!cur)
> > + return 0;
>
> Hmm, I don't think this condition is correct.
>
> If we have this topology:
>
>
> bridge0
> / | \
> / | \
> / | \
> dummy0 vlan1 vlan2
> | \
> dummy1 dummy2
>
> We end up with the expected lower/upper levels for all devices:
>
> | device | upper | lower |
> |---------+-------+-------|
> | dummy0 | 2 | 1 |
> | dummy1 | 3 | 1 |
> | dummy2 | 3 | 1 |
> | vlan1 | 2 | 2 |
> | vlan2 | 2 | 2 |
> | bridge0 | 1 | 3 |
>
>
> If we then add macvlan0 on top of bridge0:
>
>
> macvlan0
> |
> |
> bridge0
> / | \
> / | \
> / | \
> dummy0 vlan1 vlan2
> | \
> dummy1 dummy2
>
>
> we can observe that __netdev_update_upper_level is only called for
> some of the devices under bridge0. I added a perf probe:
>
> # perf probe -a '__netdev_update_upper_level dev->name:string'
>
> which gets hit for bridge0 (called directly by
> __netdev_upper_dev_link) and then dummy0, vlan1, dummy1. It is never
> called for vlan2 and dummy2.
>
> After this, we have the following levels (*):
>
> | device | upper | lower |
> |----------+-------+-------|
> | dummy0 | 3 | 1 |
> | dummy1 | 4 | 1 |
> | dummy2 | 3 | 1 |
> | vlan1 | 3 | 2 |
> | vlan2 | 2 | 2 |
> | bridge0 | 2 | 3 |
> | macvlan0 | 1 | 4 |
>
> For dummy0, dummy1, vlan1, the upper level has increased by 1, as
> expected. For dummy2 and vlan2, it's still the same, which is wrong.
>
>
> (*) observed easily by adding another probe:
>
> # perf probe -a 'dev_get_stats dev->name:string dev->upper_level dev->lower_level'
>
> and running "ip link"
>
> Or you can just add prints and recompile, of course :)
>
Thank you so much, I found a bug very easily with your test config.
I will fix this bug in a v5 patch.
> > + next = dev_stack[--cur];
> > + niter = iter_stack[cur];
> > + }
> > +
> > + now = next;
> > + iter = niter;
> > }
> >
> > return 0;
>
> --
> Sabrina
Thank you,
Taehee Yoo
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