Re: Macvlan WARNiNGS about duplicate sysfs filenames (Was [GIT] Networking)

[Andres Freund <andres@anarazel.de>]

On 2014-09-09 15:43:55 -0700, Cong Wang wrote:
> On Mon, Sep 8, 2014 at 2:25 PM, Andres Freund <andres@anarazel.de> wrote:
> > Hi,
> >
> > (don't have netdev archived, thus answering here, sorry)
> >
> > On 2014-09-07 16:41:09 -0700, David Miller wrote:
> >> Alexander Y. Fomichev (1):
> >>       net: prevent of emerging cross-namespace symlinks
> >
> 
> Since you are quoting this change, are you saying it causes
> the following kernel warning?

I thought it might be a likely candidate; but I'm not sure at all. I'll
verify it as soon as I can reboot the machine a couple of times (end of
week-ish).

> > I'm seeing WARNINGs like:
> > [ 1005.269134] ------------[ cut here ]------------
> > [ 1005.269148] WARNING: CPU: 6 PID: 4213 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0x80()
> > [ 1005.269150] sysfs: cannot create duplicate filename '/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/eth0/upper_mv-eth0'
> 
> 
> Is there a network device named upper_mv-eth0 existed in your system
> before you created macvlan?

No, there wasn't any. Afaics, the sequence is:
1) macvlan mv-eth0 is created in global namespace
2) mv-eth0 is moved (by systemd-nsspawn) into a new network
   namespace. Leaving a dangling symlink in the host namespace
/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/eth0/upper_mv-eth0 pointing toward
../mv-eth0
which doesn't exist in the external namespace. The new namespace seems
to have broken 'lower_bond0' symlink as well

This seems to be the case (and probably the actual root cause) in
slightly earlier kernels as well.
What changed seems to be that:
3) macvlan mv-eth0 is destroyed in the namespace (potentially while
   tearing it down)
4) Now there's a broken symlink that doesn't make sense in any namespace
5) mv-eth0 can't be created anew

It seems that 3-5 didn't happen that way on older kernels. The most
recent where it's not persistently broken is 3.16.0-rc7-00007 -
31dab719f. The oldest where I know it's reproducible is
3.17.0-rc4-andres-00135-g35af256.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
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