FYI, we noticed the following commit:

https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git wb-buf-throttle-v6
commit 2f0a58af6c7396b8a8ee191955c4886b54240974 ("writeback: throttle buffered writeback")

in testcase: boot

on test machine: qemu-system-x86_64 -enable-kvm -cpu kvm64,+ssse3 -smp 2 -m 8G

caused below changes:


+--------------------------------------+------------+------------+
|                                      | 0ac0f3e57c | 2f0a58af6c |
+--------------------------------------+------------+------------+
| boot_successes                       | 6          | 0          |
| boot_failures                        | 0          | 8          |
| INFO:suspicious_RCU_usage            | 0          | 8          |
| message:INFO:suspicious_RCU_usage    | 0          | 0.0        |
| pattern:INFO:suspicious_RCU_usage    | 0          | 0          |
| calltrace:disk_events_workfn         | 0          | 8          |
| message:calltrace:disk_events_workfn | 0          | 0.0        |
| pattern:calltrace:disk_events_workfn | 0          | 0          |
+--------------------------------------+------------+------------+



[   16.775948] cdrom: Uniform CD-ROM driver Revision: 3.20
[   16.803762] 
[   16.804540] ===============================
[   16.805952] [ INFO: suspicious RCU usage. ]
[   16.807334] 4.8.0-rc4-00008-g2f0a58a #1 Not tainted
[   16.812162] -------------------------------
[   16.813593] include/linux/cgroup.h:435 suspicious rcu_dereference_check() usage!
[   16.816429] 
[   16.816429] other info that might help us debug this:
[   16.816429] 
[   16.819251] 
[   16.819251] rcu_scheduler_active = 1, debug_locks = 0
[   16.821484] 3 locks held by kworker/1:1/36:
[   16.822892]  #0:  ("events_freezable_power_efficient"){.+.+..}, at: [<ffffffff810fc9d9>] process_one_work+0x151/0x4ee
[   16.826754]  #1:  ((&(&ev->dwork)->work)){+.+...}, at: [<ffffffff810fc9d9>] process_one_work+0x151/0x4ee
[   16.830373]  #2:  (&(&q->__queue_lock)->rlock){-.....}, at: [<ffffffff81789b1d>] cfq_set_request+0x5e/0x2a3
[   16.834046] 
[   16.834046] stack backtrace:
[   16.835770] CPU: 1 PID: 36 Comm: kworker/1:1 Not tainted 4.8.0-rc4-00008-g2f0a58a #1
[   16.838266] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
[   16.841039] Workqueue: events_freezable_power_ disk_events_workfn
[   16.843020]  0000000000000000 ffff880254c738e8 ffffffff8178ed3b ffff880254c6c940
[   16.846044]  0000000000000001 ffff880254c73918 ffffffff81123472 ffff880254c6c940
[   16.849044]  ffffffff84091180 0000000000000003 ffff880238ceb400 ffff880254c73938
[   16.852026] Call Trace:
[   16.853010]  [<ffffffff8178ed3b>] dump_stack+0x82/0xb8
[   16.854640]  [<ffffffff81123472>] lockdep_rcu_suspicious+0xf7/0x100
[   16.856504]  [<ffffffff817873f4>] bio_blkcg+0x89/0x93
[   16.858096]  [<ffffffff817891f0>] check_blkcg_changed+0x58/0x1b8
[   16.859905]  [<ffffffff81125fa7>] ? lock_acquire+0x125/0x1be
[   16.861647]  [<ffffffff81125fa7>] ? lock_acquire+0x125/0x1be
[   16.863355]  [<ffffffff811238d3>] ? lock_acquired+0xfc/0x2f2
[   16.865093]  [<ffffffff81789b1d>] ? cfq_set_request+0x5e/0x2a3
[   16.866878]  [<ffffffff81789b90>] cfq_set_request+0xd1/0x2a3
[   16.868479]  [<ffffffff82efb493>] ? _raw_spin_unlock_irq+0x2c/0x3b
[   16.869796]  [<ffffffff81124a52>] ? trace_hardirqs_on_caller+0x17c/0x198
[   16.871203]  [<ffffffff81124a7b>] ? trace_hardirqs_on+0xd/0xf
[   16.872428]  [<ffffffff82efb498>] ? _raw_spin_unlock_irq+0x31/0x3b
[   16.873723]  [<ffffffff8176dd78>] ? ioc_create_icq+0x15e/0x175
[   16.874933]  [<ffffffff81763fe3>] elv_set_request+0x1f/0x24
[   16.876164]  [<ffffffff8176856d>] get_request+0x38f/0x77f
[   16.877360]  [<ffffffff8111b59c>] ? add_wait_queue_exclusive+0x44/0x44
[   16.878676]  [<ffffffff817689c2>] blk_get_request+0x65/0xa8
[   16.879939]  [<ffffffff81c692df>] ide_cd_queue_pc+0x76/0x19d
[   16.881184]  [<ffffffff8112539e>] ? __lock_acquire+0x679/0xed1
[   16.882366]  [<ffffffff81c695ee>] cdrom_check_status+0x51/0x53
[   16.883625]  [<ffffffff81c6a27e>] ide_cdrom_check_events_real+0x20/0x3f
[   16.884999]  [<ffffffff82579f94>] cdrom_update_events+0x18/0x21
[   16.886292]  [<ffffffff82579faf>] cdrom_check_events+0x12/0x1f
[   16.887580]  [<ffffffff81c68317>] idecd_check_events+0x1c/0x1e
[   16.888812]  [<ffffffff81778d12>] disk_check_events+0x47/0x103
[   16.890038]  [<ffffffff81778dea>] disk_events_workfn+0x1c/0x1e
[   16.891338]  [<ffffffff810fcafa>] process_one_work+0x272/0x4ee
[   16.892599]  [<ffffffff810fd247>] worker_thread+0x1eb/0x2c9
[   16.893835]  [<ffffffff810fd05c>] ? rescuer_thread+0x2b3/0x2b3
[   16.895099]  [<ffffffff81101dd4>] kthread+0xc5/0xcd
[   16.896197]  [<ffffffff82efbf2f>] ret_from_fork+0x1f/0x40
[   16.897331]  [<ffffffff81101d0f>] ? kthread_create_on_node+0x1b0/0x1b0
[   16.899392] Loading iSCSI transport class v2.0-870.
[   16.915828] rdac: device handler registered






Thanks,
Kernel Test Robot