Message-ID: <20160726141955.GA16315@yexl-desktop>
Date:	Tue, 26 Jul 2016 22:19:55 +0800
From:	kernel test robot <xiaolong.ye@...el.com>
To:	Jens Axboe <axboe@...com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...com>,
	Jens Axboe <axboe@...nel.dk>, lkp@...org
Subject: [lkp] [writeback]  f5f3499492: INFO: suspicious RCU usage. ]


FYI, we noticed the following commit:

https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git wb-buf-throttle
commit f5f34994926d55cfbd26a045b48d02dcb345a182 ("writeback: throttle buffered writeback")

in testcase: boot

on test machine: 2 threads qemu-system-x86_64 -enable-kvm -cpu Haswell,+smep,+smap with 360M memory

caused below changes:


+---------------------------+------------+------------+
|                           | df4982ad1c | f5f3499492 |
+---------------------------+------------+------------+
| boot_successes            | 12         | 0          |
| boot_failures             | 0          | 12         |
| INFO:suspicious_RCU_usage | 0          | 12         |
+---------------------------+------------+------------+



[   28.200242] cdrom: Uniform CD-ROM driver Revision: 3.20
[   28.244319] 
[   28.245661] ===============================
[   28.247682] [ INFO: suspicious RCU usage. ]
[   28.249476] 4.7.0-00008-gf5f3499 #101 Not tainted
[   28.251157] -------------------------------
[   28.254588] include/linux/cgroup.h:434 suspicious rcu_dereference_check() usage!
[   28.274190] 
[   28.274190] other info that might help us debug this:
[   28.274190] 
[   28.288807] 
[   28.288807] rcu_scheduler_active = 1, debug_locks = 0
[   28.292385] 3 locks held by kworker/0:1/26:
[   28.294192]  #0:  ("events_freezable_power_efficient"){.+.+..}, at: [<ffffffff810f9ca8>] process_one_work+0x151/0x4ee
[   28.306687]  #1:  ((&(&ev->dwork)->work)){+.+...}, at: [<ffffffff810f9ca8>] process_one_work+0x151/0x4ee
[   28.329794]  #2:  (&(&q->__queue_lock)->rlock){-.-...}, at: [<ffffffff81772b14>] cfq_set_request+0x5c/0x2a5
[   28.337672] 
[   28.337672] stack backtrace:
[   28.339702] CPU: 0 PID: 26 Comm: kworker/0:1 Not tainted 4.7.0-00008-gf5f3499 #101
[   28.342183] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
[   28.356755] Workqueue: events_freezable_power_ disk_events_workfn
[   28.369882]  0000000000000000 ffff8800327bb900 ffffffff81777cb0 ffff8800327b46c0
[   28.379442]  0000000000000001 ffff8800327bb930 ffffffff811204e3 ffff8800327b46c0
[   28.383092]  ffffffff8408eda0 0000000000000003 ffff8800293bf800 ffff8800327bb950
[   28.386009] Call Trace:
[   28.390208]  [<ffffffff81777cb0>] dump_stack+0x82/0xb8
[   28.400642]  [<ffffffff811204e3>] lockdep_rcu_suspicious+0xf7/0x100
[   28.413613]  [<ffffffff8177081d>] bio_blkcg+0x89/0x93
[   28.421902]  [<ffffffff81771f86>] check_blkcg_changed+0x58/0x1b8
[   28.428860]  [<ffffffff81122ffe>] ? lock_acquire+0x13d/0x1d6
[   28.430802]  [<ffffffff81122ffe>] ? lock_acquire+0x13d/0x1d6
[   28.440532]  [<ffffffff8112095c>] ? lock_acquired+0xfc/0x30a
[   28.452564]  [<ffffffff81772b14>] ? cfq_set_request+0x5c/0x2a5
[   28.464870]  [<ffffffff81772b87>] cfq_set_request+0xcf/0x2a5
[   28.468666]  [<ffffffff82ed3c23>] ? _raw_spin_unlock_irq+0x2c/0x3b
[   28.471321]  [<ffffffff81121af3>] ? trace_hardirqs_on_caller+0x17c/0x198
[   28.473692]  [<ffffffff81121b1c>] ? trace_hardirqs_on+0xd/0xf
[   28.475559]  [<ffffffff82ed3c28>] ? _raw_spin_unlock_irq+0x31/0x3b
[   28.486686]  [<ffffffff8175743e>] ? ioc_create_icq+0x15e/0x175
[   28.499220]  [<ffffffff8174d7f8>] elv_set_request+0x1c/0x21
[   28.510515]  [<ffffffff81751c58>] get_request+0x333/0x728
[   28.513620]  [<ffffffff8111864f>] ? add_wait_queue_exclusive+0x44/0x44
[   28.516428]  [<ffffffff817520b1>] blk_get_request+0x64/0x88
[   28.518591]  [<ffffffff81c4951f>] ide_cd_queue_pc+0x76/0x19d
[   28.526508]  [<ffffffff81122614>] ? __lock_acquire+0x84e/0xe6f
[   28.538786]  [<ffffffff81c4982e>] cdrom_check_status+0x51/0x53
[   28.551108]  [<ffffffff81c4a4b8>] ide_cdrom_check_events_real+0x20/0x3f
[   28.564849]  [<ffffffff8255dd26>] cdrom_update_events+0x18/0x21
[   28.577281]  [<ffffffff8255dd41>] cdrom_check_events+0x12/0x1f
[   28.589660]  [<ffffffff81c48567>] idecd_check_events+0x1c/0x1e
[   28.601911]  [<ffffffff81761ff9>] disk_check_events+0x47/0x103
[   28.614128]  [<ffffffff817620d1>] disk_events_workfn+0x1c/0x1e
[   28.625378]  [<ffffffff810f9dc9>] process_one_work+0x272/0x4ee
[   28.636520]  [<ffffffff810fa516>] worker_thread+0x1eb/0x2c9
[   28.647289]  [<ffffffff810fa32b>] ? rescuer_thread+0x2b3/0x2b3
[   28.658462]  [<ffffffff810ff10c>] kthread+0xc5/0xcd
[   28.668254]  [<ffffffff82ed46af>] ret_from_fork+0x1f/0x40
[   28.679078]  [<ffffffff810ff047>] ? cpumask_check+0x35/0x35
[   28.698194] Loading iSCSI transport class v2.0-870.
[   28.723094] rdac: device handler registered


FYI, raw QEMU command line is:

	qemu-system-x86_64 -enable-kvm -cpu Haswell,+smep,+smap -kernel /pkg/linux/x86_64-allyesdebian/gcc-6/f5f34994926d55cfbd26a045b48d02dcb345a182/vmlinuz-4.7.0-00008-gf5f3499 -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-lkp-wsx03-quantal-x86_64-5/boot-1-quantal-core-x86_64.cgz-f5f34994926d55cfbd26a045b48d02dcb345a182-20160726-103825-1y2og70-0.yaml ARCH=x86_64 kconfig=x86_64-allyesdebian branch=linux-devel/devel-catchup-201607261201 commit=f5f34994926d55cfbd26a045b48d02dcb345a182 BOOT_IMAGE=/pkg/linux/x86_64-allyesdebian/gcc-6/f5f34994926d55cfbd26a045b48d02dcb345a182/vmlinuz-4.7.0-00008-gf5f3499 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-lkp-wsx03-quantal-x86_64/quantal-core-x86_64.cgz/x86_64-allyesdebian/gcc-6/f5f34994926d55cfbd26a045b48d02dcb345a182/0 LKP_SERVER=inn 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 systemd.log_level=err ignore_loglevel earlyprintk=ttyS0,115200 console=ttyS0,115200 console=tty0 vga=normal rw ip=::::vm-lkp-wsx03-quantal-x86_64-5::dhcp drbd.minor_count=8'  -initrd /fs/sdc1/initrd-vm-lkp-wsx03-quantal-x86_64-5 -m 872 -smp 2 -device e1000,netdev=net0 -netdev user,id=net0 -boot order=nc -no-reboot -watchdog i6300esb -rtc base=localtime -pidfile /dev/shm/kboot/pid-vm-lkp-wsx03-quantal-x86_64-5 -serial file:/dev/shm/kboot/serial-vm-lkp-wsx03-quantal-x86_64-5 -daemonize -display none -monitor null 





Thanks,
Xiaolong

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