netdev - Re: 2.6.35-rc2-git1 - net/mac80211/sta_info.c:125 invoked rcu_dereference

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Message-ID: <1275981969.3706.1.camel@jlt3.sipsolutions.net>
Date:	Tue, 08 Jun 2010 09:26:09 +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: 2.6.35-rc2-git1 - net/mac80211/sta_info.c:125 invoked
 rcu_dereference_check() without protection!

On Mon, 2010-06-07 at 16:59 -0700, Paul E. McKenney wrote:
> On Mon, Jun 07, 2010 at 02:25:44PM -0400, Miles Lane wrote:
> > [   43.478812] [ INFO: suspicious rcu_dereference_check() usage. ]
> > [   43.478815] ---------------------------------------------------
> > [   43.478820] net/mac80211/sta_info.c:125 invoked
> > rcu_dereference_check() without protection!
> > [   43.478824]
> > [   43.478824] other info that might help us debug this:
> > [   43.478826]
> > [   43.478829]
> > [   43.478830] rcu_scheduler_active = 1, debug_locks = 1
> > [   43.478834] no locks held by NetworkManager/4017.
> 
> Hmmm...  Johannes's update has been merged, and it requires that callers
> either be in an RCU read-side critical section or hold either the
> ->sta_lock or the ->sta_mtx, and this thread does none of this.
> 
> Johannes, any thoughts?
> 
> 							Thanx, Paul
> 
> > [   43.478837] stack backtrace:
> > [   43.478842] Pid: 4017, comm: NetworkManager Not tainted 2.6.35-rc2-git1 #8
> > [   43.478846] Call Trace:
> > [   43.478849]  <IRQ>  [<ffffffff81064e9c>] lockdep_rcu_dereference+0x9d/0xa5
> > [   43.478876]  [<ffffffffa010cb3c>] sta_info_get_bss+0x71/0x12d [mac80211]
> > [   43.478889]  [<ffffffffa010cc0d>] ieee80211_find_sta+0x15/0x2f [mac80211]
> > [   43.478902]  [<ffffffffa019ae16>] iwlagn_tx_queue_reclaim+0xe7/0x1bb [iwlagn]

iwlwifi wasn't using rcu protection here -- already sent a patch fixing
it. My mistake, I  think. Thanks for checking :)

johannes

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