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Message-ID: <AANLkTim2Z=f0-=-+FEWPAdGrMdQXFWcQbKi0JCs_1KGK@mail.gmail.com>
Date:	Tue, 5 Oct 2010 12:05:13 +0200
From:	Zdenek Kabelac <zdenek.kabelac@...il.com>
To:	Valdis.Kletnieks@...edu
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: mmotm 2010-08-11 - RCU whinge during very early boot

2010/8/12  <Valdis.Kletnieks@...edu>:
> On Wed, 11 Aug 2010 16:10:49 PDT, akpm@...ux-foundation.org said:
>> The mm-of-the-moment snapshot 2010-08-11-16-10 has been uploaded to
>>
>>    http://userweb.kernel.org/~akpm/mmotm/
>
> Throws a RCU complaint.  Hopefully somebody on the cc: list knows what it is about...
>
> [    0.026136] CPU0: Intel(R) Core(TM)2 Duo CPU     P8700  @ 2.53GHz stepping 0a
> [    0.028399] NMI watchdog enabled, takes one hw-pmu counter.
> [    0.030019] lockdep: fixing up alternatives.
> [    0.031178]
> [    0.031179] ===================================================
> [    0.031182] [ INFO: suspicious rcu_dereference_check() usage. ]
> [    0.031184] ---------------------------------------------------
> [    0.031187] kernel/sched.c:618 invoked rcu_dereference_check() without protection!
> [    0.031189]
> [    0.031189] other info that might help us debug this:
> [    0.031190]
> [    0.031192]
> [    0.031193] rcu_scheduler_active = 1, debug_locks = 1
> [    0.031195] 3 locks held by kworker/0:0/4:
> [    0.031197]  #0:  (events){+.+.+.}, at: [<ffffffff810504ca>] process_one_work+0x1b6/0x37d
> [    0.031210]  #1:  ((&c_idle.work)){+.+.+.}, at: [<ffffffff810504ca>] process_one_work+0x1b6/0x37d
> [    0.031217]  #2:  (&rq->lock){-.-...}, at: [<ffffffff81b5f9b8>] init_idle+0x2b/0x114
> [    0.031225]
> [    0.031226] stack backtrace:
> [    0.031229] Pid: 4, comm: kworker/0:0 Not tainted 2.6.35-mmotm0811 #1
> [    0.031232] Call Trace:
> [    0.031237]  [<ffffffff810661eb>] lockdep_rcu_dereference+0x9d/0xa5
> [    0.031242]  [<ffffffff8102b751>] task_group+0x7b/0x8a
> [    0.031246]  [<ffffffff81b5f9b8>] ? init_idle+0x2b/0x114
> [    0.031250]  [<ffffffff8102b775>] set_task_rq+0x15/0x6e
> [    0.031253]  [<ffffffff81b5fa5e>] init_idle+0xd1/0x114
> [    0.031257]  [<ffffffff81b5fb44>] fork_idle+0x8e/0x9d
> [    0.031261]  [<ffffffff81b5de6f>] do_fork_idle+0x17/0x28
> [    0.031265]  [<ffffffff8105052b>] process_one_work+0x217/0x37d
> [    0.031269]  [<ffffffff810504ca>] ? process_one_work+0x1b6/0x37d
> [    0.031273]  [<ffffffff81b5de58>] ? do_fork_idle+0x0/0x28
> [    0.031277]  [<ffffffff81051775>] worker_thread+0x17e/0x251
> [    0.031281]  [<ffffffff810515f7>] ? worker_thread+0x0/0x251
> [    0.031285]  [<ffffffff8105544a>] kthread+0x7d/0x85
> [    0.031290]  [<ffffffff81003554>] kernel_thread_helper+0x4/0x10
> [    0.031295]  [<ffffffff81558d80>] ? restore_args+0x0/0x30
> [    0.031299]  [<ffffffff810553cd>] ? kthread+0x0/0x85
> [    0.031303]  [<ffffffff81003550>] ? kernel_thread_helper+0x0/0x10
> [    0.031333] Booting Node   0, Processors  #1 Ok.
> [    0.103111] NMI watchdog enabled, takes one hw-pmu counter.
> [    0.104013] Brought up 2 CPUs
>

I'm still seeing this INFO message on my vanilla 2.6.36-rc kernel.

----------------------

ftrace: converting mcount calls to 0f 1f 44 00 00
ftrace: allocating 16045 entries in 63 pages
Setting APIC routing to flat
..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
CPU0: Intel(R) Core(TM)2 Duo CPU     T7500  @ 2.20GHz stepping 0a
NMI watchdog enabled, takes one hw-pmu counter.
lockdep: fixing up alternatives.

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
kernel/sched.c:618 invoked rcu_dereference_check() without protection!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
3 locks held by kworker/0:0/4:
 #0:  (events){+.+.+.}, at: [<ffffffff8106e78e>] process_one_work+0x12e/0x560
 #1:  ((&c_idle.work)){+.+.+.}, at: [<ffffffff8106e78e>]
process_one_work+0x12e/0x560
 #2:  (&rq->lock){......}, at: [<ffffffff814772c3>] init_idle+0x30/0x12c

stack backtrace:
Pid: 4, comm: kworker/0:0 Not tainted 2.6.36-rc6-00085-g6e34025 #1
Call Trace:
 [<ffffffff81089c1b>] lockdep_rcu_dereference+0xbb/0xc0
 [<ffffffff8103e7d5>] set_task_rq+0x2f5/0x300
 [<ffffffff81477374>] init_idle+0xe1/0x12c
 [<ffffffff81477769>] fork_idle+0x90/0x9f
 [<ffffffff81048dfa>] ? enqueue_entity+0x13a/0x430
 [<ffffffff81482789>] ? sub_preempt_count+0x59/0x60
 [<ffffffff814752f5>] do_fork_idle+0x1c/0x2d
 [<ffffffff8106e7fa>] process_one_work+0x19a/0x560
 [<ffffffff8106e78e>] ? process_one_work+0x12e/0x560
 [<ffffffff814752d9>] ? do_fork_idle+0x0/0x2d
 [<ffffffff81070189>] worker_thread+0x169/0x340
 [<ffffffff81070020>] ? worker_thread+0x0/0x340
 [<ffffffff810752e6>] kthread+0xa6/0xb0
 [<ffffffff81004014>] kernel_thread_helper+0x4/0x10
 [<ffffffff8147efcb>] ? _raw_spin_unlock_irq+0x3b/0x60
 [<ffffffff8147f600>] ? restore_args+0x0/0x30
 [<ffffffff81075240>] ? kthread+0x0/0xb0
 [<ffffffff81004010>] ? kernel_thread_helper+0x0/0x10
Booting Node   0, Processors  #1 Ok.
TSC synchronization [CPU#0 -> CPU#1]:
Measured 399476 cycles TSC warp between CPUs, turning off TSC clock.
Marking TSC unstable due to check_tsc_sync_source failed
NMI watchdog enabled, takes one hw-pmu counter.
Brought up 2 CPUs
Total of 2 processors activated (8781.86 BogoMIPS).
regulator: core version 0.5
regulator: dummy:
Time:  7:44:09  Date: 10/05/10


Zdenek
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