Subject: net/ipv4/route.c:645 suspicious rcu_dereference_check() usage!

From: [email-masked]
Date: Mon, 10 Sep 2012 09:44:38 +0100

I've not seen this reported yet, so here's a warning that happens
occasionally:

[192979.475833] 
[192979.475840] ===============================
[192979.475841] [ INFO: suspicious RCU usage. ]
[192979.475844] 3.6.0-rc2+ #33 Not tainted
[192979.475846] -------------------------------
[192979.475848] net/ipv4/route.c:645 suspicious rcu_dereference_check() usage!
[192979.475850] 
[192979.475850] other info that might help us debug this:
[192979.475850] 
[192979.475853] 
[192979.475853] rcu_scheduler_active = 1, debug_locks = 0
[192979.475856] 2 locks held by firefox-bin/4634:
[192979.475858]  #0:  (slock-AF_INET){+.-...}, at: [<ffffffff814261b4>] release_sock+0x34/0x1e0
[192979.475870]  #1:  (fnhe_lock){+.-...}, at: [<ffffffff81461c94>] update_or_create_fnhe.isra.30+0x44/0x480
[192979.475878] 
[192979.475878] stack backtrace:
[192979.475881] Pid: 4634, comm: firefox-bin Not tainted 3.6.0-rc2+ #33
[192979.475883] Call Trace:
[192979.475891]  [<ffffffff810903cd>] lockdep_rcu_suspicious+0xfd/0x130
[192979.475895]  [<ffffffff81461e8e>] update_or_create_fnhe.isra.30+0x23e/0x480
[192979.475899]  [<ffffffff814624ba>] __ip_rt_update_pmtu.isra.31+0x6a/0xb0
[192979.475903]  [<ffffffff81465038>] ip_rt_update_pmtu+0x48/0xd0
[192979.475907]  [<ffffffff814759b1>] inet_csk_update_pmtu+0x31/0x80
[192979.475912]  [<ffffffff8148b663>] tcp_v4_mtu_reduced+0x33/0xd0
[192979.475915]  [<ffffffff814888be>] tcp_release_cb+0x5e/0xb0
[192979.475919]  [<ffffffff81426289>] release_sock+0x109/0x1e0
[192979.475922]  [<ffffffff81479037>] tcp_sendmsg+0x527/0x1030
[192979.475927]  [<ffffffff814a4d9d>] inet_sendmsg+0xed/0x240
[192979.475931]  [<ffffffff814a4cb0>] ? inet_autobind+0x70/0x70
[192979.475934]  [<ffffffff81424e8a>] ? sock_update_classid+0xaa/0x370
[192979.475937]  [<ffffffff81424eb8>] ? sock_update_classid+0xd8/0x370
[192979.475941]  [<ffffffff8141ee1b>] sock_sendmsg+0xab/0xe0
[192979.475946]  [<ffffffff814222be>] sys_sendto+0x11e/0x160
[192979.475951]  [<ffffffff8153e547>] ? sysret_check+0x1b/0x56
[192979.475956]  [<ffffffff8125849e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[192979.475960]  [<ffffffff8153e522>] system_call_fastpath+0x16/0x1b

-- 
Chris Wilson, Intel Open Source Technology Centre