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Message-ID: <1272181534.3614.1.camel@jlt3.sipsolutions.net> Date: Sun, 25 Apr 2010 09:45:34 +0200 From: Johannes Berg <johannes@...solutions.net> To: paulmck@...ux.vnet.ibm.com Cc: Miles Lane <miles.lane@...il.com>, Vivek Goyal <vgoyal@...hat.com>, Eric Paris <eparis@...hat.com>, Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>, nauman@...gle.com, eric.dumazet@...il.com, netdev@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>, Gui Jianfeng <guijianfeng@...fujitsu.com>, Li Zefan <lizf@...fujitsu.com> Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage On Sat, 2010-04-24 at 19:34 -0700, Paul E. McKenney wrote: > > [ 51.912282] [ INFO: suspicious rcu_dereference_check() usage. ] > > [ 51.912285] --------------------------------------------------- > > [ 51.912289] net/mac80211/sta_info.c:886 invoked > > rcu_dereference_check() without protection! > > [ 51.912293] > > [ 51.912293] other info that might help us debug this: > > [ 51.912295] > > [ 51.912298] > > [ 51.912298] rcu_scheduler_active = 1, debug_locks = 1 > > [ 51.912302] no locks held by wpa_supplicant/3951. > > [ 51.912305] > > [ 51.912306] stack backtrace: > > [ 51.912310] Pid: 3951, comm: wpa_supplicant Not tainted 2.6.34-rc5-git3 #22 > > [ 51.912314] Call Trace: > > [ 51.912317] <IRQ> [<ffffffff81067fbe>] lockdep_rcu_dereference+0x9d/0xa5 > > [ 51.912345] [<ffffffffa014f9ae>] > > ieee80211_find_sta_by_hw+0x46/0x10f [mac80211] > > [ 51.912358] [<ffffffffa014fa8e>] ieee80211_find_sta+0x17/0x19 [mac80211] > > [ 51.912373] [<ffffffffa01e50f2>] iwl_tx_queue_reclaim+0xdb/0x1b1 [iwlcore] > > [ 51.912380] [<ffffffff8106842b>] ? mark_lock+0x2d/0x235 > > [ 51.912391] [<ffffffffa0252f1c>] iwl5000_rx_reply_tx+0x4a9/0x556 [iwlagn] > > [ 51.912399] [<ffffffff8120a353>] ? is_swiotlb_buffer+0x2e/0x3b > > [ 51.912407] [<ffffffffa024bbf4>] iwl_rx_handle+0x163/0x2b5 [iwlagn] > > [ 51.912414] [<ffffffff81068904>] ? trace_hardirqs_on_caller+0xfa/0x13f > > [ 51.912422] [<ffffffffa024c3ac>] iwl_irq_tasklet+0x2bb/0x3c0 [iwlagn] > > [ 51.912429] [<ffffffff810411f3>] tasklet_action+0xa7/0x10f > > [ 51.912435] [<ffffffff81042205>] __do_softirq+0x144/0x252 > > [ 51.912442] [<ffffffff81003a8c>] call_softirq+0x1c/0x34 > > [ 51.912447] [<ffffffff810050e4>] do_softirq+0x38/0x80 > > [ 51.912452] [<ffffffff81041cd2>] irq_exit+0x45/0x94 > > [ 51.912457] [<ffffffff81004829>] do_IRQ+0xad/0xc4 > > [ 51.912463] [<ffffffff810cbbd3>] ? might_fault+0x63/0xb3 > > [ 51.912470] [<ffffffff813cfb93>] ret_from_intr+0x0/0xf > > [ 51.912474] <EOI> [<ffffffff810cbbd3>] ? might_fault+0x63/0xb3 > > [ 51.912484] [<ffffffff8106a75d>] ? lock_release+0x208/0x215 > > [ 51.912490] [<ffffffff810cbc1c>] might_fault+0xac/0xb3 > > [ 51.912495] [<ffffffff810cbbd3>] ? might_fault+0x63/0xb3 > > [ 51.912501] [<ffffffff812025e3>] __clear_user+0x15/0x59 > > [ 51.912508] [<ffffffff8100b2bc>] save_i387_xstate+0x9c/0x1bc > > [ 51.912515] [<ffffffff81002276>] do_signal+0x240/0x686 > > [ 51.912521] [<ffffffff81002b9c>] ? sysret_check+0x27/0x62 > > [ 51.912527] [<ffffffff8106891e>] ? trace_hardirqs_on_caller+0x114/0x13f > > [ 51.912533] [<ffffffff813cec80>] ? trace_hardirqs_on_thunk+0x3a/0x3f > > [ 51.912539] [<ffffffff810026e3>] do_notify_resume+0x27/0x5f > > [ 51.912545] [<ffffffff813cec80>] ? trace_hardirqs_on_thunk+0x3a/0x3f > > [ 51.912551] [<ffffffff81002e86>] int_signal+0x12/0x17 > > This is a repeat from last time that confused me at the time. I could > do a hacky "fix" by putting an RCU read-side critical section around > the for_each_sta_info() in ieee80211_find_sta_by_hw(), but I do not > understand this code well enough to feel comfortable doing so. > > Johannes, any enlightenment? The station locking is a tad confusing, but I've added the right annotations already, should be coming to a kernel near you soon (i.e. are in net-2.6 right now). johannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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