linux-kernel - 2.6.35-stable/ppc64/p7: suspicious rcu_dereference_check() usage detected during 2.6.35-stable boot

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Message-Id: <1280739132.15317.9.camel@subratamodak.linux.ibm.com>
Date:	Mon, 02 Aug 2010 14:22:12 +0530
From:	Subrata Modak <subrata@...ux.vnet.ibm.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Li Zefan <lizf@...fujitsu.com>,
	Linuxppc-dev <Linuxppc-dev@...abs.org>,
	sachinp <sachinp@...ux.vnet.ibm.com>,
	DIVYA PRAKASH <dipraksh@...ux.vnet.ibm.com>
Subject: 2.6.35-stable/ppc64/p7: suspicious rcu_dereference_check() usage
	detected during 2.6.35-stable boot

Hi,

The following suspicious rcu_dereference_check() usage is detected
during 2.6.35-stable boot on my ppc64/p7 machine:

==================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
kernel/sched.c:616 invoked rcu_dereference_check() without protection!
other info that might help us debug this:

rcu_scheduler_active = 1, debug_locks = 0
1 lock held by swapper/1:
 #0:  (&rq->lock){-.....}, at: [<c0000000007ca2f8>] .init_idle+0x78/0x4a8
stack backtrace:
Call Trace:
[c000000f392bf990] [c000000000014f04] .show_stack+0xb0/0x1a0 (unreliable)
[c000000f392bfa50] [c0000000007c87b4] .dump_stack+0x28/0x3c
[c000000f392bfad0] [c000000000103e1c] .lockdep_rcu_dereference+0xbc/0xe4
[c000000f392bfb70] [c0000000007ca434] .init_idle+0x1b4/0x4a8
[c000000f392bfc30] [c0000000007cad04] .fork_idle+0xa4/0xd0
[c000000f392bfe30] [c000000000aefaac] .smp_prepare_cpus+0x23c/0x2f4
[c000000f392bfed0] [c000000000ae1424] .kernel_init+0xec/0x32c
[c000000f392bff90] [c000000000033f40] .kernel_thread+0x54/0x70
==================================================

Please note that this was reported earlier on 2.6.34-rc6:
http://marc.info/?l=linux-kernel&m=127313031922395&w=2,
The issue was fixed with:
	commit 1ce7e4ff24fe338438bc7837e02780f202bf202b
	Author: Li Zefan <lizf@...fujitsu.com>
	Date:   Fri Apr 23 10:35:52 2010 +0800
	cgroup: Check task_lock in task_subsys_state()

According to:
	http://lkml.org/lkml/2010/7/1/883,
	commit dc61b1d65e353d638b2445f71fb8e5b5630f2415
	Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
	Date:   Tue Jun 8 11:40:42 2010 +0200
	sched: Fix PROVE_RCU vs cpu_cgroup
should have fixed this. But this is reproducible on 2.6.35-stable.

Please also see the config file attached.

Regards--
Subrata


View attachment "config-2.6.35-ppc64-p7" of type "text/plain" (104563 bytes)