linux-kernel - Re: [GIT PULL rcu/next] rcu commits for 2.6.40

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Date:	Wed, 11 May 2011 09:56:35 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40

On Tue, May 10, 2011 at 9:54 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Tue, May 10, 2011 at 01:52:52PM -0700, Yinghai Lu wrote:
>> On 05/10/2011 12:32 PM, Paul E. McKenney wrote:
>> > On Tue, May 10, 2011 at 11:04:57AM -0700, Yinghai Lu wrote:
>> >> On 05/10/2011 01:56 AM, Paul E. McKenney wrote:
>> >>> On Mon, May 09, 2011 at 02:09:21PM -0700, Yinghai Lu wrote:
>> >>>> On Mon, May 9, 2011 at 12:36 AM, Ingo Molnar <mingo@...e.hu> wrote:
>> >>>>>
>> >>>>> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
>> >>>>>
>> >>>>>> Hello, Ingo,
>> >>>>>>
>> >>>>>> This pull request covers RCU chnages for 2.6.40.  The major new features
>> >>>>>> are RCU priority boosting and the addition of kfree_rcu(), the latter
>> >>>>>> courtesy of Lai Jiangshan.  These two features cover well over half
>> >>>>>> of the commits.  There are a number of smaller features and bug fixes.
>> >>>>>> All have been sent to LKML in the following batches:
>> >>>>>>
>> >>>>>> 0.    https://lkml.org/lkml/2011/2/22/660: RCU priority boosting preview
>> >>>>>> 1.    https://lkml.org/lkml/2011/5/1/19: RCU priority boosting, kfree_rcu()
>> >>>>>> 2.    https://lkml.org/lkml/2011/5/2/40: More uses of kfree_rcu()
>> >>>>>> 3.    https://lkml.org/lkml/2011/5/8/60: miscellaneous
>> >>>>>>
>> >>>>>> The kfree_rcu() uses in the pull request have Acked-by:s from the
>> >>>>>> maintainers.  I have some additional kfree_rcu() requests that lack
>> >>>>>> Acked-by:s, and I will deal with these later.
>> >>>>>>
>> >>>>>> These channges are available in the -rcu git repository at:
>> >>>>>>
>> >>>>>>   git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/next
>> >>>>>
>> >>>>> Pulled, thanks a lot Paul!
>> >>>>>
>> >>>>
>> >>>> it seems with this one in tip, my 8 sockets test setup will report cpu stall.
>> >>>>
>> >>>> after hard code to enable rcu_cpu_stall_suppress
>> >>>>
>> >>>> Index: linux-2.6/kernel/rcutree.c
>> >>>> ===================================================================
>> >>>> --- linux-2.6.orig/kernel/rcutree.c
>> >>>> +++ linux-2.6/kernel/rcutree.c
>> >>>> @@ -174,7 +174,7 @@ module_param(blimit, int, 0);
>> >>>>  module_param(qhimark, int, 0);
>> >>>>  module_param(qlowmark, int, 0);
>> >>>>
>> >>>> -int rcu_cpu_stall_suppress __read_mostly;
>> >>>> +int rcu_cpu_stall_suppress __read_mostly = 1;
>> >>>>  module_param(rcu_cpu_stall_suppress, int, 0644);
>> >>>>
>> >>>>  static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
>> >>>>
>> >>>> will get system hang after pnp ACPI init.
>> >>>
>> >>> Could you please send the stack traces from the RCU CPU stall?  Also,
>> >>> you do have ce31332d3c77532d6ea97ddcb475a2b02dd358b4 applied, correct?
>> >>>
>> >>>                                                   Thanx, Paul
>> >>
>> >> Do not have time to bisect it at this point.
>> >
>> > Could you please send the stack traces from the RCU CPU stall?
>
> Thank you!  OK, so CPU 0 has not been responding, despite resched IPIs.
> Everyone is idle, except for CPU 124, which detected the stall, and
> possibly CPU 0, which has csum_partial_copy_generic() on the stack, though
> that looks like a backtrace error to me.  The fact that it hangs if you
> disable RCU CPU stall detection leads me to believe that something real
> is being detected.

the problem is that now I can not disable RCU CPU stall detection any more.

Thanks

Yinghai
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