linux-kernel - Re: [tip:core/rcu] rcu: Add diagnostic check for a possible CPU-hotplug race

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Date:	Sun, 2 Aug 2009 22:27:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	mingo@...hat.com, hpa@...or.com, paulmck@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/rcu] rcu: Add diagnostic check for a possible
	CPU-hotplug race


* tip-bot for Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> Commit-ID:  7256cf0e83bf018be8a81806593aaef7f2437f0b
> Gitweb:     http://git.kernel.org/tip/7256cf0e83bf018be8a81806593aaef7f2437f0b
> Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> AuthorDate: Sun, 2 Aug 2009 10:21:10 -0700
> Committer:  Ingo Molnar <mingo@...e.hu>
> CommitDate: Sun, 2 Aug 2009 21:31:28 +0200
> 
> rcu: Add diagnostic check for a possible CPU-hotplug race
> 
> Complain if the RCU softirq code ever runs on a CPU that has
> not yet been announced to RCU as being online.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> LKML-Reference: <new-submission>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>

FYI, the new warning triggered in -tip testing:

calling  tracer_alloc_buffers+0x0/0x296 @ 1
initcall tracer_alloc_buffers+0x0/0x296 returned 0 after 0 usecs
calling  init_trace_printk+0x0/0x7 @ 1
initcall init_trace_printk+0x0/0x7 returned 0 after 0 usecs
lockdep: fixing up alternatives.
Booting processor 1 APIC 0x1 ip 0x6000
Initializing CPU#1
masked ExtINT on CPU#1
Calibrating delay using timer specific routine.. 4021.85 BogoMIPS (lpj=6700572)
CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
CPU: L2 Cache: 512K (64 bytes/line)
CPU: Physical Processor ID: 0
CPU: Processor Core ID: 1
mce: CPU supports 5 MCE banks
CPU1: AMD Athlon(tm) 64 X2 Dual Core Processor 3800+ stepping 02
Brought up 2 CPUs
Total of 2 processors activated (8043.58 BogoMIPS).
------------[ cut here ]------------
WARNING: at kernel/rcutree.c:1140 __rcu_process_callbacks+0x2c/0xb9()
Hardware name: System Product Name
Pid: 0, comm: swapper Not tainted 2.6.31-rc5-tip #280
Call Trace:
 [<c105229d>] warn_slowpath_common+0x60/0x90
 [<c10522df>] warn_slowpath_null+0x12/0x15
 [<c1091f70>] __rcu_process_callbacks+0x2c/0xb9
 [<c1092021>] rcu_process_callbacks+0x24/0x42
 [<c105737c>] __do_softirq+0xbc/0x16f
 [<c105746a>] do_softirq+0x3b/0x5f
 [<c10575c2>] irq_exit+0x3a/0x6d
 [<c10318cb>] smp_apic_timer_interrupt+0x74/0x82
 [<c101f0af>] apic_timer_interrupt+0x2f/0x40
 [<c101d7c2>] ? cpu_idle+0x77/0x99
 [<c10370e0>] ? native_safe_halt+0xa/0xc
 [<c10248cf>] default_idle+0x80/0xd1
 [<c101d7c8>] cpu_idle+0x7d/0x99
 [<c1f806f1>] start_secondary+0xf7/0xf9
---[ end trace 4eaa2a86a8e2da22 ]---
CPU0 attaching sched-domain:
 domain 0: span 0-1 level MC
  groups: 0 1
CPU1 attaching sched-domain:
 domain 0: span 0-1 level MC
  groups: 1 0
device: 'platform': device_add
khelper used greatest stack depth: 6632 bytes left
bus: 'platform': registered
Registering sysdev class 'cpu'
calling  init_cpufreq_transition_notifier_list+0x0/0x18 @ 1
initcall init_cpufreq_transition_notifier_list+0x0/0x18 returned 0 after 0 usecs
calling  net_ns_init+0x0/0x120 @ 1
initcall net_ns_init+0x0/0x120 returned 0 after 0 usecs

with the attached config.

	Ingo

View attachment "config" of type "text/plain" (62462 bytes)