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From: Ilia Mirkin on 5 Aug 2010 13:40
On Thu, Jul 1, 2010 at 6:18 PM, Paul E. McKenney
<paulmck(a)linux.vnet.ibm.com> wrote:
> On Thu, Jul 01, 2010 at 08:21:43AM -0400, Miles Lane wrote:
>> [ 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 = 1
>> 3 locks held by swapper/1:
>> � #0: �(cpu_add_remove_lock){+.+.+.}, at: [<ffffffff81042914>]
>> cpu_maps_update_begin+0x12/0x14
>> � #1: �(cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8104294f>]
>> cpu_hotplug_begin+0x27/0x4e
>> � #2: �(&rq->lock){-.-...}, at: [<ffffffff812f8502>] init_idle+0x2b/0x114
>
> Hello, Miles!
>
> I believe that this one is fixed by commit dc61b1d6 in -tip.

Hi Paul,

Looks like that commit made it into 2.6.35:

git tag -l --contains dc61b1d65e353d638b2445f71fb8e5b5630f2415 v2.6.35*
v2.6.35
v2.6.35-rc4
v2.6.35-rc5
v2.6.35-rc6

However I still get:

[ 0.051203] CPU0: AMD QEMU Virtual CPU version 0.12.4 stepping 03
[ 0.052999] lockdep: fixing up alternatives.
[ 0.054105]
[ 0.054106] ===================================================
[ 0.054999] [ INFO: suspicious rcu_dereference_check() usage. ]
[ 0.054999] ---------------------------------------------------
[ 0.054999] kernel/sched.c:616 invoked rcu_dereference_check()
without protection
!
[ 0.054999]
[ 0.054999] other info that might help us debug this:
[ 0.054999]
[ 0.054999]
[ 0.054999] rcu_scheduler_active = 1, debug_locks = 1
[ 0.054999] 3 locks held by swapper/1:
[ 0.054999] #0: (cpu_add_remove_lock){+.+.+.}, at:
[<ffffffff814be933>] cpu_up+
0x42/0x6a
[ 0.054999] #1: (cpu_hotplug.lock){+.+.+.}, at:
[<ffffffff810400d8>] cpu_hotplu
g_begin+0x2a/0x51
[ 0.054999] #2: (&rq->lock){-.-...}, at: [<ffffffff814be2f7>]
init_idle+0x2f/0x
113
[ 0.054999]
[ 0.054999] stack backtrace:
[ 0.054999] Pid: 1, comm: swapper Not tainted 2.6.35 #1
[ 0.054999] Call Trace:
[ 0.054999] [<ffffffff81068054>] lockdep_rcu_dereference+0x9b/0xa3
[ 0.054999] [<ffffffff810325c3>] task_group+0x7b/0x8a
[ 0.054999] [<ffffffff810325e5>] set_task_rq+0x13/0x40
[ 0.054999] [<ffffffff814be39a>] init_idle+0xd2/0x113
[ 0.054999] [<ffffffff814be78a>] fork_idle+0xb8/0xc7
[ 0.054999] [<ffffffff81068717>] ? mark_held_locks+0x4d/0x6b
[ 0.054999] [<ffffffff814bcebd>] do_fork_idle+0x17/0x2b
[ 0.054999] [<ffffffff814bc89b>] native_cpu_up+0x1c1/0x724
[ 0.054999] [<ffffffff814bcea6>] ? do_fork_idle+0x0/0x2b
[ 0.054999] [<ffffffff814be876>] _cpu_up+0xac/0x127
[ 0.054999] [<ffffffff814be946>] cpu_up+0x55/0x6a
[ 0.054999] [<ffffffff81ab562a>] kernel_init+0xe1/0x1ff
[ 0.054999] [<ffffffff81003854>] kernel_thread_helper+0x4/0x10
[ 0.054999] [<ffffffff814c353c>] ? restore_args+0x0/0x30
[ 0.054999] [<ffffffff81ab5549>] ? kernel_init+0x0/0x1ff
[ 0.054999] [<ffffffff81003850>] ? kernel_thread_helper+0x0/0x10
[ 0.056074] Booting Node 0, Processors #1lockdep: fixing up alternatives.
[ 0.130045] #2lockdep: fixing up alternatives.
[ 0.203089] #3 Ok.
[ 0.275286] Brought up 4 CPUs
[ 0.276005] Total of 4 processors activated (16017.17 BogoMIPS).

--
Ilia Mirkin
imirkin(a)alum.mit.edu
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