netdev - Re: A race in register

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Date:	Tue, 3 May 2011 16:41:59 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Kalle Valo <kvalo@...rom.com>
Cc:	netdev@...r.kernel.org, linux-wireless@...r.kernel.org
Subject: Re: A race in register_netdevice()

On Wed, 04 May 2011 02:18:11 +0300
Kalle Valo <kvalo@...rom.com> wrote:

> Hi Stephen,
> 
> Stephen Hemminger <shemminger@...tta.com> writes:
> 
> > On Fri, 29 Apr 2011 01:36:37 +0300
> > Kalle Valo <kvalo@...rom.com> wrote:
> >
> >> there seems to be a race in register_netdevice(), which is reported here:
> >> 
> >> https://bugzilla.kernel.org/show_bug.cgi?id=15606
> >> 
> >> This is visible at least with flimflam and ath6kl. Basically what
> >> happens is this:
> >> 
> >> Apr 29 00:21:35 roska flimflamd[2598]: src/udev.c:add_net_device() 
> >> Apr 29 00:21:35 roska flimflamd[2598]: connman_inet_ifname: SIOCGIFNAME(index
> >> 4): No such device
> >> Apr 29 00:21:45 roska flimflamd[2598]: src/rtnl.c:rtnl_message() buf
> >> 0xbfefda3c len 1004
> >> Apr 29 00:21:45 roska flimflamd[2598]: src/rtnl.c:rtnl_message()
> >> NEWLINK len 1004 type 16 flags 0x0000 seq 0
> 
> [...]
> 
> >> I have confirmed that both of these patches fix the issue. Now I'm
> >> wondering which one is the best way forward. Or is there a better way
> >> to fix this?
> >> 
> >
> > I see no problem with moving this.
> > SIOCGIFNAME should not need to hold rtnl.
> 
> I'm having difficulties of fixing the race and exploring other
> options. Is there any particular issue why SIOCGIFNAME should not take
> rtnl?

None really, but the answer given by SIOCGIFNAME is going to race
anyway. I.e if ioctl returns a value, by the time user space sees it
the result may have changed.
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