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

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Date:	Mon, 19 Apr 2010 21:25:29 -0400
From:	Eric Paris <eparis@...hat.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Eric Paris <eparis@...isplace.org>,
	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, 2010-04-19 at 16:01 -0700, Paul E. McKenney wrote:

> Yep, different code path to the same location.  Does the following
> patch help?
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 2836f18139267ea918ed2cf39023fb0eb38c4361
> Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Date:   Mon Apr 19 15:59:50 2010 -0700
> 
>     rcu: fix RCU lockdep splat on freezer_fork path
>     
>     Add an RCU read-side critical section to suppress this false positive.
>     
>     Located-by: Eric Paris <eparis@...isplace.org>
>     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

That one is also fixed so feel free to add a tested or something from
me.  But we've got another, weeeee!  If there some way I could get all
of these at once?

[    0.045164] ===================================================
[    0.047002] [ INFO: suspicious rcu_dereference_check() usage. ]
[    0.048002] ---------------------------------------------------
[    0.049012] include/linux/cgroup.h:533 invoked rcu_dereference_check() without protection!
[    0.051087] 
[    0.051088] other info that might help us debug this:
[    0.051088] 
[    0.057011] 
[    0.057011] rcu_scheduler_active = 1, debug_locks = 0
[    0.059046] no locks held by watchdog/0/5.
[    0.060002] 
[    0.060003] stack backtrace:
[    0.061003] Pid: 5, comm: watchdog/0 Not tainted 2.6.34-rc4-next-20100415+ #104
[    0.063011] Call Trace:
[    0.063654]  [<ffffffff8108652f>] lockdep_rcu_dereference+0xaf/0xc0
[    0.065009]  [<ffffffff810b53f0>] ? watchdog+0x0/0xa0
[    0.066006]  [<ffffffff8104d01b>] __sched_setscheduler+0x3ab/0x430
[    0.067005]  [<ffffffff810b53f0>] ? watchdog+0x0/0xa0
[    0.068004]  [<ffffffff8104d0be>] sched_setscheduler+0xe/0x10
[    0.070009]  [<ffffffff810b541a>] watchdog+0x2a/0xa0
[    0.071004]  [<ffffffff810b53f0>] ? watchdog+0x0/0xa0
[    0.072007]  [<ffffffff810714ec>] kthread+0xac/0xc0
[    0.073005]  [<ffffffff81087ff0>] ? trace_hardirqs_on_caller+0xc0/0x240
[    0.074006]  [<ffffffff8100bc24>] kernel_thread_helper+0x4/0x10
[    0.075005]  [<ffffffff814fee54>] ? restore_args+0x0/0x30
[    0.076004]  [<ffffffff81071440>] ? kthread+0x0/0xc0
[    0.077004]  [<ffffffff8100bc20>] ? kernel_thread_helper+0x0/0x10



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