linux-kernel - Re: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference

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Date:	Mon, 12 Apr 2010 20:47:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Eric Paris <eparis@...isplace.org>
Cc:	paulmck@...ux.vnet.ibm.com, Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: INFO: suspicious rcu_dereference_check() usage - 
 include/linux/cgroup.h:492 invoked rcu_dereference_check() without 
 protection!

On Mon, 2010-04-12 at 14:44 -0400, Eric Paris wrote:
> On Wed, Mar 10, 2010 at 11:28 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:

> I know you indicated this was fixed in mainline and I see that set of
> commits objects, but I'm seeing the below spew from linux-next today.
> 
> tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> tag: next-20100412
> commit: bbeecf185fe464ccd7ee97ce6d3646ad686995b4
> 
> [    0.035602] ===================================================
> [    0.036003] [ INFO: suspicious rcu_dereference_check() usage. ]
> [    0.037006] ---------------------------------------------------
> [    0.038004] include/linux/cgroup.h:533 invoked
> rcu_dereference_check() without protection!
> [    0.039003]
> [    0.039004] other info that might help us debug this:
> [    0.039004]
> [    0.040003]
> [    0.040004] rcu_scheduler_active = 1, debug_locks = 0
> [    0.041004] no locks held by swapper/0.
> [    0.042003]
> [    0.042004] stack backtrace:
> [    0.043005] Pid: 0, comm: swapper Not tainted 2.6.34-rc3-next-20100412+ #65
> [    0.044003] Call Trace:
> [    0.045015]  [<ffffffff8108584f>] lockdep_rcu_dereference+0xaf/0xc0
> [    0.046010]  [<ffffffff81044812>] set_task_cpu+0x2d2/0x370

Oh, right, I still have to sort that out.

I need to figure out how all that scheduler and cgroup muck interact to
fix this.
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