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Date:	Sat, 23 Aug 2014 23:39:39 -0400
From:	Pranith Kumar <pranith@...ech.edu>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Amit Shah <amit.shah@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>, dvhart@...ux.intel.com,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Silas Boyd-Wickizer <sbw@....edu>
Subject: Re: [PATCH tip/core/rcu 1/2] rcu: Parallelize and economize NOCB
 kthread wakeups

On Sat, Aug 23, 2014 at 11:23 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Sat, Aug 23, 2014 at 08:26:10PM -0400, Pranith Kumar wrote:
>> On Sat, Aug 23, 2014 at 12:51 PM, Paul E. McKenney
>> <paulmck@...ux.vnet.ibm.com> wrote:
>>
>> > It might well!  Another possibility is that the early_initcall function
>> > doing the synchronize_rcu() is happening before the early_initcall
>> > creating the RCU grace-period kthreads.
>> >
>> > Seems like we need to close both holes.  Let's see how your patch works
>> > for Amit, and I am testing a patch for the possible early_initcall
>> > ordering issue.
>>
>> I checked the init call which is calling synchronize_rcu():
>> subsys_initcall(pm_sysrq_init); this is being called after
>> early_initcall.
>>
>> The order of initcalls is early, core, postcore, arch, subsys, fs,
>> device, late. So I guess that is ok.
>>
>> I wonder why it was not showing up in 12.04. I have a dual boot. Will
>> test it out and see if I can find something.
>
> Me, I am wondering about 7,000 callbacks being registered during early
> boot time.  ;-)
>


This is the backtrace for most of the callbacks:

[    4.612103] ------------[ cut here ]------------
[    4.613340] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_plugin.h:2115
__call_rcu_nocb_enqueue+0x58/0x283()
[    4.615975] Modules linked in:
[    4.616000] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W     3.16.0+ #76
[    4.616000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS Bochs 01/01/2011
[    4.616000]  0000000000000000 ffffffff81803c20 ffffffff813c5213
0000000000000000
[    4.616000]  ffffffff81803c58 ffffffff810388aa ffffffff8108aac8
ffff88001f9cce40
[    4.616000]  ffff88001f5b6c08 0000000000000000 0000000000000286
ffffffff81803c68
[    4.616000] Call Trace:
[    4.616000]  [<ffffffff813c5213>] dump_stack+0x4e/0x7a
[    4.616000]  [<ffffffff810388aa>] warn_slowpath_common+0x7f/0x98
[    4.616000]  [<ffffffff8108aac8>] ? __call_rcu_nocb_enqueue+0x58/0x283
[    4.616000]  [<ffffffff81038976>] warn_slowpath_null+0x1a/0x1c
[    4.616000]  [<ffffffff8108aac8>] __call_rcu_nocb_enqueue+0x58/0x283
[    4.616000]  [<ffffffff81129f3a>] ? unreferenced_object+0x4f/0x4f
[    4.616000]  [<ffffffff8108d913>] __call_rcu+0xcd/0x32b
[    4.616000]  [<ffffffff8108de66>] call_rcu+0x1b/0x1d
[    4.616000]  [<ffffffff8112a301>] put_object+0x41/0x44
[    4.616000]  [<ffffffff8112a70a>] delete_object_full+0x29/0x2c
[    4.616000]  [<ffffffff813c2166>] kmemleak_free+0x25/0x43
[    4.616000]  [<ffffffff81120cca>] slab_free_hook+0x1d/0x63
[    4.616000]  [<ffffffff811228c6>] kmem_cache_free+0x52/0x154
[    4.616000]  [<ffffffff8124aa01>] ? acpi_os_release_object+0xe/0x12
[    4.616000]  [<ffffffff8124aa01>] acpi_os_release_object+0xe/0x12
[    4.616000]  [<ffffffff8126c567>] acpi_ps_free_op+0x25/0x27
[    4.616000]  [<ffffffff8126b81f>] acpi_ps_create_op+0x135/0x209
[    4.616000]  [<ffffffff8126b1f2>] acpi_ps_parse_loop+0x1d3/0x575
[    4.616000]  [<ffffffff8126bff2>] acpi_ps_parse_aml+0xa0/0x277
[    4.616000]  [<ffffffff81267d7f>] acpi_ns_one_complete_parse+0xfc/0x11b
[    4.616000]  [<ffffffff81267dd1>] acpi_ns_parse_table+0x33/0x38
[    4.616000]  [<ffffffff81267755>] acpi_ns_load_table+0x4c/0x8b
[    4.616000]  [<ffffffff81ad6797>] acpi_load_tables+0x9d/0x15d
[    4.616000]  [<ffffffff81ad5b44>] acpi_early_init+0x73/0xfe
[    4.616000]  [<ffffffff81aa5e8e>] start_kernel+0x3a9/0x40a
[    4.616000]  [<ffffffff81aa5120>] ? early_idt_handlers+0x120/0x120
[    4.616000]  [<ffffffff81aa54ba>] x86_64_start_reservations+0x2a/0x2c
[    4.616000]  [<ffffffff81aa55f8>] x86_64_start_kernel+0x13c/0x149
[    4.616000] ---[ end trace 8dbfee90ca96696c ]---


-- 
Pranith
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