Patrick McHardy wrote:

quoted

Its harmless since its a read lock, which can be nested. I actually
don't see any need for qdisc_tree_lock at all, all changes and all
walking is done under the RTNL, which is why I've removed it in
my (upcoming) patches. I suggest to leave it as is for now so I
don't need to change the __qdisc_lookup back to qdisc_lookup in
2.6.22.

Alexey just explained to me why we do need qdisc_tree_lock in private
mail. While dumping only the first skb is filled under the RTNL,
while filling further skbs we don't hold the RTNL anymore. So I will
probably have to drop that patch.

What we could do is replace the netlink cb_lock spinlock by a
user-supplied mutex (supplied to netlink_kernel_create, rtnl_mutex
in this case). That would put the entire dump under the rtnl and
allow us to get rid of qdisc_tree_lock and avoid the need to take
dev_base_lock during qdisc dumping. Same in other spots like
rtnl_dump_ifinfo, inet_dump_ifaddr, ...

What do you think?