linux-kernel - [lkp] [writeback] 9340837195: INFO: suspicious RCU usage. ]

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Date:	Fri, 22 Jul 2016 16:47:25 +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]  9340837195: 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 93408371951a8c076c58a532e3e7e14969e5e015 ("writeback: throttle buffered writeback")

in testcase: boot

on test machine: 1 threads qemu-system-x86_64 -enable-kvm -cpu SandyBridge with 320M memory

caused below changes:


+---------------------------+------------+--------------------+
|                           | fd9e8f2822 |     9340837195     |
+---------------------------+------------+--------------------+
| boot_successes            | 6          | 4                  |
| boot_failures             | 0          | 30                 |
| INFO:suspicious_RCU_usage | 0          | 30                 |
| backtrace:do_mount        | 0          | 28                 |
| backtrace:SyS_mount       | 0          | 28                 |
| timestamp.last            | 0          | 3676.8605620000003 |
| backtrace:do_sys_open     | 0          | 2                  |
| backtrace:SyS_open        | 0          | 2                  |
+---------------------------+------------+--------------------+



[   19.168560] input: ImExPS/2 BYD TouchPad as /devices/platform/i8042/serio1/input/input3
[   21.175977] 
[   21.177141] ===============================
[   21.178757] [ INFO: suspicious RCU usage. ]
[   21.180364] 4.7.0-rc7-00008-g9340837 #246 Not tainted
[   21.182098] -------------------------------
[   21.183728] include/linux/cgroup.h:434 suspicious rcu_dereference_check() usage!
[   21.186972] 
[   21.186972] other info that might help us debug this:
[   21.186972] 
[   21.190687] 
[   21.190687] rcu_scheduler_active = 1, debug_locks = 0
[   21.193455] 4 locks held by mount/2419:
[   21.195030]  #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8122cba7>] __blkdev_get+0x96/0x3d0
[   21.198794]  #1:  (floppy_mutex){+.+.+.}, at: [<ffffffff81761c3d>] floppy_open+0x38/0x303
[   21.202444]  #2:  (open_lock){+.+.+.}, at: [<ffffffff81761c4b>] floppy_open+0x46/0x303
[   21.205831]  #3:  (floppy_lock){......}, at: [<ffffffff815561de>] cfq_set_request+0x5c/0x32c
[   21.209547] 
[   21.209547] stack backtrace:
[   21.211888] CPU: 0 PID: 2419 Comm: mount Not tainted 4.7.0-rc7-00008-g9340837 #246
[   21.214848] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
[   21.218069]  0000000000000000 ffff88000c7cb778 ffffffff8155bee7 ffff88000b038040
[   21.221473]  0000000000000001 ffff88000c7cb7a8 ffffffff810e8aff ffff88000b88c008
[   21.224926]  ffff88000b038040 0000000000000003 ffff88000d0a8008 ffff88000c7cb868
[   21.228228] Call Trace:
[   21.229486]  [<ffffffff8155bee7>] dump_stack+0x86/0xc0
[   21.231276]  [<ffffffff810e8aff>] lockdep_rcu_suspicious+0xf7/0x100
[   21.233302]  [<ffffffff8155555a>] check_blkcg_changed+0x202/0x402
[   21.235246]  [<ffffffff810ec591>] ? lock_acquire+0x188/0x223
[   21.237097]  [<ffffffff815561de>] ? cfq_set_request+0x5c/0x32c
[   21.238987]  [<ffffffff81556251>] cfq_set_request+0xcf/0x32c
[   21.240916]  [<ffffffff81ccfe9f>] ? _raw_spin_unlock_irq+0x2c/0x3d
[   21.242879]  [<ffffffff810ea8b1>] ? trace_hardirqs_on_caller+0x17e/0x19a
[   21.244951]  [<ffffffff810ea8da>] ? trace_hardirqs_on+0xd/0xf
[   21.246855]  [<ffffffff81ccfe9f>] ? _raw_spin_unlock_irq+0x2c/0x3d
[   21.248886]  [<ffffffff81538330>] ? ioc_create_icq+0x15b/0x172
[   21.250814]  [<ffffffff8152ce10>] elv_set_request+0x1c/0x21
[   21.252668]  [<ffffffff81531003>] get_request+0x54d/0xa5d
[   21.254488]  [<ffffffff810e0a43>] ? wake_up_bit+0x2a/0x2a
[   21.256319]  [<ffffffff815349a9>] blk_queue_bio+0x1ba/0x4dc
[   21.258096]  [<ffffffff8153279d>] generic_make_request+0xbd/0x15b
[   21.260066]  [<ffffffff81532943>] submit_bio+0x108/0x113
[   21.261895]  [<ffffffff817618a4>] __floppy_read_block_0+0xcb/0x116
[   21.263905]  [<ffffffff810ea71d>] ? mark_held_locks+0x5e/0x74
[   21.265831]  [<ffffffff81ccfe5d>] ? _raw_spin_unlock_irqrestore+0x48/0x5e
[   21.267931]  [<ffffffff810ea8b1>] ? trace_hardirqs_on_caller+0x17e/0x19a
[   21.270019]  [<ffffffff81761794>] ? floppy_resume+0x3f/0x3f
[   21.271937]  [<ffffffff81761a98>] floppy_revalidate+0x1a9/0x1bc
[   21.273925]  [<ffffffff8122bf75>] check_disk_change+0x52/0x5e
[   21.275815]  [<ffffffff81761e80>] floppy_open+0x27b/0x303
[   21.277644]  [<ffffffff8122cc19>] __blkdev_get+0x108/0x3d0
[   21.279503]  [<ffffffff8122d1bb>] ? blkdev_get+0x2da/0x2fe
[   21.284992]  [<ffffffff8122d0a8>] blkdev_get+0x1c7/0x2fe
[   21.286812]  [<ffffffff81214827>] ? mntput_no_expire+0xdd/0x350
[   21.288780]  [<ffffffff81214ac7>] ? mntput+0x2d/0x2f
[   21.290542]  [<ffffffff811fe291>] ? path_put+0x1e/0x21
[   21.292319]  [<ffffffff8122d212>] blkdev_get_by_path+0x33/0x69
[   21.294226]  [<ffffffff811f82d6>] mount_bdev+0x48/0x197
[   21.296766]  [<ffffffff812ade04>] ? ext4_calculate_overhead+0x2bd/0x2bd
[   21.298783]  [<ffffffff812aa4f9>] ext4_mount+0x15/0x17
[   21.300537]  [<ffffffff811f8f02>] mount_fs+0x14/0x8d
[   21.302228]  [<ffffffff81213cae>] vfs_kern_mount+0x6b/0x133
[   21.304137]  [<ffffffff81216ebc>] do_mount+0xa4d/0xb53
[   21.305915]  [<ffffffff811b4e44>] ? strndup_user+0x3f/0x6b
[   21.307738]  [<ffffffff812171ed>] SyS_mount+0x77/0x9f
[   21.309470]  [<ffffffff81cd067c>] entry_SYSCALL_64_fastpath+0x1f/0xbd
[   21.376317] blk_update_request: I/O error, dev fd0, sector 0


FYI, raw QEMU command line is:

	qemu-system-x86_64 -enable-kvm -cpu SandyBridge -kernel /pkg/linux/x86_64-nfsroot/gcc-6/93408371951a8c076c58a532e3e7e14969e5e015/vmlinuz-4.7.0-rc7-00008-g9340837 -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-kbuild-yocto-x86_64-32/rand_boot-1-yocto-minimal-x86_64.cgz-93408371951a8c076c58a532e3e7e14969e5e015-20160722-42999-h2wrj2-0.yaml ARCH=x86_64 kconfig=x86_64-nfsroot branch=block/wb-buf-throttle commit=93408371951a8c076c58a532e3e7e14969e5e015 BOOT_IMAGE=/pkg/linux/x86_64-nfsroot/gcc-6/93408371951a8c076c58a532e3e7e14969e5e015/vmlinuz-4.7.0-rc7-00008-g9340837 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-kbuild-yocto-x86_64/yocto-minimal-x86_64.cgz/x86_64-nfsroot/gcc-6/93408371951a8c076c58a532e3e7e14969e5e015/0 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 earlyprintk=ttyS0,115200 console=ttyS0,115200 console=tty0 vga=normal rw ip=::::vm-kbuild-yocto-x86_64-32::dhcp drbd.minor_count=8'  -initrd /fs/sdh1/initrd-vm-kbuild-yocto-x86_64-32 -m 320 -smp 1 -device e1000,netdev=net0 -netdev user,id=net0 -boot order=nc -no-reboot -watchdog i6300esb -rtc base=localtime -drive file=/fs/sdh1/disk0-vm-kbuild-yocto-x86_64-32,media=disk,if=virtio -pidfile /dev/shm/kboot/pid-vm-kbuild-yocto-x86_64-32 -serial file:/dev/shm/kboot/serial-vm-kbuild-yocto-x86_64-32 -daemonize -display none -monitor null 





Thanks,
Xiaolong

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