Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"

From: Yinghai Lu <yinghai@kernel.org>
To: paulmck@linux.vnet.ibm.com
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com,
	tglx@linutronix.de, mingo@elte.hu
Subject: Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"
Date: Mon, 23 May 2011 15:58:45 -0700	[thread overview]
Message-ID: <4DDAE6A5.6060701@kernel.org> (raw)
In-Reply-To: <4DDAE5FA.2030303@kernel.org>

On 05/23/2011 03:55 PM, Yinghai Lu wrote:
> On 05/23/2011 03:01 PM, Yinghai Lu wrote:
>> On 05/23/2011 02:25 PM, Paul E. McKenney wrote:
>>> On Mon, May 23, 2011 at 01:14:22PM -0700, Yinghai Lu wrote:
>>>> On 05/21/2011 07:08 AM, Paul E. McKenney wrote:
>>>>> On Sat, May 21, 2011 at 06:18:44AM -0700, Paul E. McKenney wrote:
>>>>>> On Fri, May 20, 2011 at 05:02:40PM -0700, Yinghai Lu wrote:
>>>>>>> On 05/20/2011 04:49 PM, Paul E. McKenney wrote:
>>>>>>>> On Fri, May 20, 2011 at 04:16:28PM -0700, Yinghai Lu wrote:
>>>>>>> ...
>>>>>>>>>
>>>>>>>>> the same one i sent out before, but let DEBUG_LOCKING_API_SELFTESTS disabled.
>>>>>>>>
>>>>>>>> OK, just to make sure I understand...  You are compiling exactly the
>>>>>>>> same kernel source tree with exactly the same .config, just with two
>>>>>>>> different versions of gcc, correct?
>>>>>>> yes.
>>>>>>>>
>>>>>>>> If so, it is quite possible that the slow one is the correct one.  :-/
>>>>>>> yeah, new version always have problem.
>>>>>>>
>>>>>>> looks like opensuse11.3 has 4.5.0 and fedora14 has 4.5.1
>>>>>>
>>>>>> OK, so fedora14 is the fast one (4.5.1) and opensuse11.3 is the slow
>>>>>> one (4.5.0), correct?
>>>>>
>>>>> And does commit c7a3786030 help?  This commit (from Peter Zijlstra)
>>>>> tidied up RCU kthreads' scheduler interactions.  The patch is below,
>>>>> though it is probably more convenient to pull it from the rcu/next
>>>>> branch of:
>>>>>
>>>>>   git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git
>>>>>
>>>
> gcc in Fedora 14 is fine with your tree.
> 

sorry, I should wait for longer to see Fedora 14 is ok.

got same warning with the one compiled from fedora 14...

[  372.937251] INFO: task rcun0:8 blocked for more than 120 seconds.
[  372.937618] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  372.956130] rcun0           D 0000000000000000     0     8      2 0x00000000
[  372.956498]  ffff882070d65e90 0000000000000046 ffff882070d64000 0000000000004000
[  372.956528]  00000000001d1f40 ffff882070d65fd8 00000000001d1f40 ffff882070d65fd8
[  372.956555]  0000000000004000 00000000001d1f40 ffff882070d18000 ffff882070d6a2b0
[  372.956581] Call Trace:
[  372.956605]  [<ffffffff810afce3>] ? __lock_release+0x166/0x16f
[  372.956624]  [<ffffffff81c229d1>] ? _raw_spin_unlock_irqrestore+0x3f/0x46
[  372.956639]  [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137
[  372.956650]  [<ffffffff810adfd5>] ? trace_hardirqs_on+0xd/0xf
[  372.956661]  [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137
[  372.956673]  [<ffffffff8109a0a5>] kthread+0x8c/0xa8
[  372.956689]  [<ffffffff81c2a754>] kernel_thread_helper+0x4/0x10
[  372.956701]  [<ffffffff81c22c80>] ? retint_restore_args+0xe/0xe
[  372.956711]  [<ffffffff8109a019>] ? __init_kthread_worker+0x5b/0x5b
[  372.956722]  [<ffffffff81c2a750>] ? gs_change+0xb/0xb
[  372.956726] INFO: lockdep is turned off.
[  492.750827] INFO: task rcun0:8 blocked for more than 120 seconds.
[  492.751150] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  492.762991] rcun0           D 0000000000000000     0     8      2 0x00000000
[  492.763264]  ffff882070d65e90 0000000000000046 ffff882070d64000 0000000000004000
[  492.763294]  00000000001d1f40 ffff882070d65fd8 00000000001d1f40 ffff882070d65fd8
[  492.763320]  0000000000004000 00000000001d1f40 ffff882070d18000 ffff882070d6a2b0
[  492.763346] Call Trace:
[  492.763359]  [<ffffffff810afce3>] ? __lock_release+0x166/0x16f
[  492.763371]  [<ffffffff81c229d1>] ? _raw_spin_unlock_irqrestore+0x3f/0x46
[  492.763382]  [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137
[  492.763393]  [<ffffffff810adfd5>] ? trace_hardirqs_on+0xd/0xf
[  492.763404]  [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137
[  492.763414]  [<ffffffff8109a0a5>] kthread+0x8c/0xa8
[  492.763427]  [<ffffffff81c2a754>] kernel_thread_helper+0x4/0x10
[  492.763439]  [<ffffffff81c22c80>] ? retint_restore_args+0xe/0xe
[  492.763449]  [<ffffffff8109a019>] ? __init_kthread_worker+0x5b/0x5b
[  492.763460]  [<ffffffff81c2a750>] ? gs_change+0xb/0xb
[  492.763463] INFO: lockdep is turned off.

if reverting PeterZ's patch will not have that warning.

Thanks