2.6.0-test4-mm6: locking imbalance with rtnl_lock/unlock?

[Jeremy Fitzhardinge]

I've been playing with Bryan O'Sullivan's netplug daemon
(http://www.red-bean.com/~bos/).  It uses netlink to look at carrier
state changes on network interfaces.

I'm seeing a problem however: after a while, all ifconfig commands just
block uninterruptably in __down().  From strace, it seems to be in:

ioctl(4, 0x8915...

which is SIOCGIFADDR.  It seems to me the down() is actually the
rtnl_lock() called at net/ipv4/devinet.c:536 in devinet_ioctl.  This
happens even when netplugd is no longer running.  It looks like someone
isn't releasing the lock.

I'm going over all the uses of rtnl_lock() to see if I can find a
problem, but no sign yet.  I wonder if someone might have broken this
recently: I'm running 2.6.0-test4-mm6, but I think Bryan is running an
older kernel (2.6.0-test4?), and hasn't seen any problems.

	J

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