netdev - Is it normal to have cross namespace symlinks?

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Message-ID: <20140821143816.48c5ad08@mad-cat.int.e5.ru>
Date:	Thu, 21 Aug 2014 14:38:16 +0400
From:	"Alexander Y. Fomichev" <git.user@...il.com>
To:	netdev@...r.kernel.org
Subject: Is it normal to have cross namespace symlinks?

Hello guys!

Recently i switched to 3.14.x stable branch and i've got a bunch of
warnings:

[   44.717746] ------------[ cut here ]------------
[   44.717750] WARNING: CPU: 1 PID: 7007 at fs/sysfs/dir.c:52
sysfs_warn_dup+0x86/0xa0() [   44.717751] sysfs: cannot create
duplicate filename
'/devices/pci0000:00/0000:00:1c.4/0000:05:00.0/net/eth1/upper_eth1'

[   37.759856] ------------[ cut here ]------------
[   37.759863] WARNING: CPU: 1 PID: 3822 at fs/sysfs/dir.c:52
sysfs_warn_dup+0x86/0xa0() [   37.759864] sysfs: cannot create
duplicate filename '/devices/virtual/net/bond0/upper_eth0'
....

It was triggered by renaming of macvlan interfaces in a freshly created
network namespaces. Just start two lxc containers one by one with
macvlans on the same lowerdev and rename devices inside containers (with
the same name) and voila.

I investigated problem a bit and i see that code in net/core/dev.c
which working with sysfs symlinks upper_dev / lower_dev is absolutely
unaware of namespaces. I mean code which uses functions
netdev_adjacent_sysfs_del,netdev_adjacent_sysfs_add
netdev_adjacent_rename_links,dev_change_name
just not takes into account that dev and adj_dev could be in a
different namespaces. If userland asks to rename interface in a
new namespace this code renames an upper_dev link
in a parent namespace accordingly. I hadn't tried but i'll
bet it works vice-versa as well. It leads to warnings i've wrote above
and also creation inside namespaces a pretty meaningless links:
/sys/devices/virtual/net/eth1/lower_eth1
-> ../../../pci0000:00/0000:00:1c.4/0000:05:00.0/net/eth1
or probably deletion of symlinks of a perfectly valid devices. 

At the same time this issue is not affecting most of current
functionality and seems like nobody cares about that. I suspect that
there's (almost) no real users of sysfs uppder_dev/lower_dev simlinks,
am i right?

-- 

Best regards.
        Alexander Y. Fomichev <Aleksandr.Fomichev@...ru>
	        +7-495-662-88-88 ext. 11346
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