quoted

Is this the same RCU problem that was fixed after 3.3 (fix a potential 
rcu_read_lock() imbalance in rt6_fill_node())? My problem does not seem 
to be ipv6-only, most traces are from IPv6 but some for ip.

It's hard to say because the ipv6 RCU problem causes the warning to
trigger somewhere away from the ipv6 code that had the RCU locking
bug.

Tested todays 3.4.0-rc2-00016-ga9e1e53 on the same with flood ping and 
still got RCU warning:

[36456.693191] 
[36456.712658] ===============================
[36456.767614] [ INFO: suspicious RCU usage. ]
[36456.822588] 3.4.0-rc2-00016-ga9e1e53 #36 Not tainted
[36456.887835] -------------------------------
[36456.942804] include/linux/netpoll.h:70 suspicious rcu_dereference_check() usage!
[36457.040083] 
[36457.040089] other info that might help us debug this:
[36457.040098] 
[36457.145306] 
[36457.145312] RCU used illegally from idle CPU!
[36457.145320] rcu_scheduler_active = 1, debug_locks = 0
[36457.288293] RCU used illegally from extended quiescent state!
[36457.363834] no locks held by swapper/0.
[36457.414221] 
[36457.414227] stack backtrace:
[36457.471471] Call Trace:
[36457.503600]  [0000000000489834] lockdep_rcu_suspicious+0xd4/0x100
[36457.583727]  [00000000006755a8] __netif_receive_skb+0x368/0xa80
[36457.661536]  [0000000000675e6c] netif_receive_skb+0x4c/0x60
[36457.734787]  [000000000063fd74] tulip_poll+0x3b4/0x6a0
[36457.802327]  [00000000006794d8] net_rx_action+0x118/0x1e0
[36457.873299]  [00000000004560fc] __do_softirq+0x9c/0x140
[36457.941984]  [000000000042b1c4] do_softirq+0x84/0xc0
[36458.007229]  [0000000000404a40] __handle_softirq+0x0/0x10
[36458.078199]  [000000000042b688] cpu_idle+0x48/0x100
[36458.142314]  [0000000000722db8] rest_init+0x160/0x188
[36458.208711]  [00000000008c87b0] start_kernel+0x32c/0x33c
[36458.278530]  [0000000000722c50] tlb_fixup_done+0x88/0x90
[36458.348346]  [0000000000000000]           (null)


-- 
Meelis Roos (mroos@linux.ee)