Return-path: Received: from he.sipsolutions.net ([78.46.109.217]:60569 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753716Ab2DLDcN (ORCPT ); Wed, 11 Apr 2012 23:32:13 -0400 Message-ID: <1334201497.3788.1.camel@jlt3.sipsolutions.net> (sfid-20120412_053217_196595_A9D189B9) Subject: Re: Suspicious RCU usage in mac80211 From: Johannes Berg To: Larry Finger Cc: wireless Date: Thu, 12 Apr 2012 05:31:37 +0200 In-Reply-To: <4F83A6DE.7070109@lwfinger.net> (sfid-20120410_052034_062782_82AB2FD8) References: <4F83A6DE.7070109@lwfinger.net> (sfid-20120410_052034_062782_82AB2FD8) Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Mon, 2012-04-09 at 22:19 -0500, Larry Finger wrote: > When running kernel 3.4-rc2 from wireless testing, I got the following logged: > > [ 2299.344437] =============================== > [ 2299.344443] [ INFO: suspicious RCU usage. ] > [ 2299.344452] 3.4.0-rc2-wl+ #222 Not tainted > [ 2299.344458] ------------------------------- > [ 2299.344466] net/mac80211/sta_info.h:449 suspicious rcu_dereference_protected() usage! > [ 2299.344472] > [ 2299.344474] other info that might help us debug this: > [ 2299.344477] > [ 2299.344484] > [ 2299.344486] rcu_scheduler_active = 1, debug_locks = 0 > [ 2299.344493] 1 lock held by swapper/1/0: > [ 2299.344499] #0: (&tid_tx->session_timer){+.-...}, at: [] > run_timer_softirq+0xfa/0x6e0 > [ 2299.344533] > [ 2299.344535] stack backtrace: > [ 2299.344544] Pid: 0, comm: swapper/1 Not tainted 3.4.0-rc2-wl+ #222 > [ 2299.344551] Call Trace: > [ 2299.344557] [] lockdep_rcu_suspicious+0xfd/0x130 > [ 2299.344651] [] sta_tx_agg_session_timer_expired+0xe3/0x100 > [mac80211] That's odd: static inline struct tid_ampdu_tx * rcu_dereference_protected_tid_tx(struct sta_info *sta, int tid) { return rcu_dereference_protected(sta->ampdu_mlme.tid_tx[tid], lockdep_is_held(&sta->lock) || lockdep_is_held(&sta->ampdu_mlme.mtx)); } sta_tx_agg_session_timer_expired calls ieee80211_stop_tx_ba_session which does: spin_lock_bh(&sta->lock); tid_tx = rcu_dereference_protected_tid_tx(sta, tid); So why would the message happen? Strange. johannes