netdev - Re: suspicious RCU usage warnings in 3.3.0

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Date:	Wed, 11 Apr 2012 18:08:53 +0300 (EEST)
From:	Meelis Roos <mroos@...ux.ee>
To:	David Miller <davem@...emloft.net>
cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: suspicious RCU usage warnings in 3.3.0

> > 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@...ux.ee)
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