linux-kernel - [sched] [ INFO: suspicious RCU usage. ]

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Date:	Tue, 28 Oct 2014 22:27:15 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, LKP <lkp@...org>,
	linux-kernel@...r.kernel.org
Subject: [sched] [ INFO: suspicious RCU usage. ]

Greetings,

0day kernel testing robot got the below dmesg and the first bad commit is

git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/urgent
commit f6a2b544517d33f6a1e428567bda96fd859ce1c9
Author:     Kirill Tkhai <ktkhai@...allels.com>
AuthorDate: Mon Oct 27 14:18:25 2014 +0400
Commit:     Peter Zijlstra <peterz@...radead.org>
CommitDate: Mon Oct 27 13:23:31 2014 +0100

    sched: Fix race between task_group and sched_task_group
    
    The race may happen when somebody is changing task_group of a forking task.
    Child's cgroup is the same as parent's after dup_task_struct() (there just
    memory copying). Also, cfs_rq and rt_rq are the same as parent's.
    
    But if parent changes its task_group before it's called cgroup_post_fork(),
    we do not reflect this situation on child. Child's cfs_rq and rt_rq remain
    the same, while child's task_group changes in cgroup_post_fork().
    
    To fix this we introduce fork() method, which calls sched_move_task() directly.
    This function changes sched_task_group on appropriate (also its logic has
    no problem with freshly created tasks, so we shouldn't introduce something
    special; we are able just to use it).
    
    Possibly, this decides the Burke Libbey's problem: https://lkml.org/lkml/2014/10/24/456
    
    Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
    Link: http://lkml.kernel.org/r/1414405105.19914.169.camel@tkhai

+---------------------------+-----------+------------+------------+
|                           | v3.18-rc2 | f6a2b54451 | 8e5859c73b |
+---------------------------+-----------+------------+------------+
| boot_successes            | 200       | 0          | 0          |
| boot_failures             | 1         | 20         | 11         |
| BUG:kernel_boot_hang      | 1         |            |            |
| INFO:suspicious_RCU_usage | 0         | 20         | 11         |
| backtrace:do_fork         | 0         | 20         | 11         |
+---------------------------+-----------+------------+------------+

[    0.060187] 
[    0.060500] ===============================
[    0.060500] ===============================
[    0.061307] [ INFO: suspicious RCU usage. ]
[    0.061307] [ INFO: suspicious RCU usage. ]
[    0.062109] 3.18.0-rc2-gf6a2b54 #404 Not tainted
[    0.062109] 3.18.0-rc2-gf6a2b54 #404 Not tainted
[    0.063049] -------------------------------

git bisect start 8e5859c73b9f45602222441a23eba899bb24c82e 522e980064c24d3dd9859e9375e17417496567cf --
git bisect  bad 259820751fd17a4b49098429c68c2c0adfd1c9ed  # 21:11      0-      2  Merge branch 'sched/core'
git bisect  bad 8c64bf8de891aa51e916b51a3f7992321ec19b63  # 21:15      0-      1  Merge branch 'sched/urgent'
git bisect  bad fd457f2bafdc4e367d1814ac395035a35980783f  # 21:27      0-      7  sched/fair: Care divide error in update_task_scan_period()
git bisect  bad fb5b330f079e243dcc831e9a3d65b9b9fbbed7f8  # 21:36      0-      1  sched/deadline: don't replenish from a !SCHED_DEADLINE entity
git bisect  bad f6a2b544517d33f6a1e428567bda96fd859ce1c9  # 21:41      0-      2  sched: Fix race between task_group and sched_task_group
# first bad commit: [f6a2b544517d33f6a1e428567bda96fd859ce1c9] sched: Fix race between task_group and sched_task_group
git bisect good cac7f2429872d3733dc3f9915857b1691da2eb2f  # 21:58     60+      1  Linux 3.18-rc2
git bisect  bad 8e5859c73b9f45602222441a23eba899bb24c82e  # 22:00      0-     11  Merge branch 'sched/wait'
git bisect good cac7f2429872d3733dc3f9915857b1691da2eb2f  # 22:05     60+      1  Linux 3.18-rc2
git bisect good 7a891e6323e963f3301e44bdeee734028e34d390  # 22:14     60+      0  Add linux-next specific files for 20141027


This script may reproduce the error.

----------------------------------------------------------------------------
#!/bin/bash

kernel=$1
initrd=quantal-core-x86_64.cgz

wget --no-clobber https://github.com/fengguang/reproduce-kernel-bug/raw/master/initrd/$initrd

kvm=(
	qemu-system-x86_64
	-cpu kvm64
	-enable-kvm
	-kernel $kernel
	-initrd $initrd
	-m 320
	-smp 2
	-net nic,vlan=1,model=e1000
	-net user,vlan=1
	-boot order=nc
	-no-reboot
	-watchdog i6300esb
	-rtc base=localtime
	-serial stdio
	-display none
	-monitor null 
)

append=(
	hung_task_panic=1
	earlyprintk=ttyS0,115200
	debug
	apic=debug
	sysrq_always_enabled
	rcupdate.rcu_cpu_stall_timeout=100
	panic=-1
	softlockup_panic=1
	nmi_watchdog=panic
	oops=panic
	load_ramdisk=2
	prompt_ramdisk=0
	console=ttyS0,115200
	console=tty0
	vga=normal
	root=/dev/ram0
	rw
	drbd.minor_count=8
)

"${kvm[@]}" --append "${append[*]}"
----------------------------------------------------------------------------

Thanks,
Fengguang

View attachment "dmesg-quantal-vp-29:20141027214255:x86_64-randconfig-c0-1027:3.18.0-rc2-gf6a2b54:404" of type "text/plain" (113675 bytes)

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