INFO: task hung in sync_inodes_sb (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 17529385 Linux 4.14.213
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12eb37a8d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f94010bb59bd4675
dashboard link: https://syzkaller.appspot.com/bug?extid=d72364f87ba3a6d6eec1
compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d72364...@syzkaller.appspotmail.com

Bluetooth: hci4 command 0x0406 tx timeout
Bluetooth: hci0 command 0x0406 tx timeout
Bluetooth: hci2 command 0x0406 tx timeout
Bluetooth: hci1 command 0x0406 tx timeout
Bluetooth: hci3 command 0x0406 tx timeout
INFO: task syz-executor.1:8047 blocked for more than 140 seconds.
Not tainted 4.14.213-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.1 D25768 8047 1 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x88b/0x1de0 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
wb_wait_for_completion fs/fs-writeback.c:222 [inline]
wb_wait_for_completion+0x118/0x170 fs/fs-writeback.c:218
sync_inodes_sb+0x173/0x880 fs/fs-writeback.c:2471
__sync_filesystem fs/sync.c:34 [inline]
sync_filesystem fs/sync.c:67 [inline]
sync_filesystem+0x12f/0x230 fs/sync.c:48
generic_shutdown_super+0x70/0x370 fs/super.c:432
kill_block_super+0x95/0xe0 fs/super.c:1161
deactivate_locked_super+0x6c/0xd0 fs/super.c:319
deactivate_super+0x7f/0xa0 fs/super.c:350
cleanup_mnt+0x186/0x2c0 fs/namespace.c:1183
task_work_run+0x11f/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x1ad/0x200 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
do_syscall_64+0x4a3/0x640 arch/x86/entry/common.c:297
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x460c47
RSP: 002b:00007ffcbc913768 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000460c47
RDX: 00000000004033a8 RSI: 0000000000000002 RDI: 00007ffcbc913810
RBP: 0000000000039919 R08: 0000000000000000 R09: 000000000000000b
R10: 0000000000000005 R11: 0000000000000246 R12: 00007ffcbc9148c0
R13: 000000000263ca60 R14: 0000000000000000 R15: 000000000003984c

Showing all locks held in the system:
2 locks held by kworker/u4:2/34:
#0: ("writeback"){+.+.}, at: [<ffffffff81373630>] process_one_work+0x6b0/0x14a0 kernel/workqueue.c:2087
#1: ((&(&wb->dwork)->work)){+.+.}, at: [<ffffffff81373666>] process_one_work+0x6e6/0x14a0 kernel/workqueue.c:2091
1 lock held by khungtaskd/1531:
#0: (tasklist_lock){.+.+}, at: [<ffffffff81430dd4>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
2 locks held by syz-executor.1/8047:
#0: (&type->s_umount_key#88){+.+.}, at: [<ffffffff818980e7>] deactivate_super+0x77/0xa0 fs/super.c:349
#1: (&bdi->wb_switch_rwsem){+.+.}, at: [<ffffffff8192dfa6>] bdi_down_write_wb_switch_rwsem fs/fs-writeback.c:338 [inline]
#1: (&bdi->wb_switch_rwsem){+.+.}, at: [<ffffffff8192dfa6>] sync_inodes_sb+0x156/0x880 fs/fs-writeback.c:2469

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 1531 Comm: khungtaskd Not tainted 4.14.213-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x283 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x13a/0x17f lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5b9/0xb40 kernel/hung_task.c:274
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff8720a96e


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 17529385 Linux 4.14.213
git tree: linux-4.14.y

console output: https://syzkaller.appspot.com/x/log.txt?x=145c7d57500000

kernel config: https://syzkaller.appspot.com/x/.config?x=f94010bb59bd4675
dashboard link: https://syzkaller.appspot.com/bug?extid=d72364f87ba3a6d6eec1
compiler: gcc (GCC) 10.1.0-syz 20200507

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=122638f7500000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=111d5eeb500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d72364...@syzkaller.appspotmail.com

NILFS (loop0): mounting unchecked fs
NILFS (loop0): recovery complete
NILFS (loop0): segctord starting. Construction interval = 5 seconds, CP frequency < 30 seconds
NILFS (loop0): unrecognized mount option "mode=00000000000000000007777"
INFO: task syz-executor694:8019 blocked for more than 140 seconds.

Not tainted 4.14.213-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor694 D29712 8019 8009 0x00000004

Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x88b/0x1de0 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
wb_wait_for_completion fs/fs-writeback.c:222 [inline]
wb_wait_for_completion+0x118/0x170 fs/fs-writeback.c:218
sync_inodes_sb+0x173/0x880 fs/fs-writeback.c:2471
__sync_filesystem fs/sync.c:34 [inline]
sync_filesystem fs/sync.c:67 [inline]
sync_filesystem+0x12f/0x230 fs/sync.c:48

nilfs_remount+0x51/0x470 fs/nilfs2/super.c:1129
do_remount_sb+0x150/0x530 fs/super.c:868
do_remount fs/namespace.c:2370 [inline]
do_mount+0x1632/0x2a00 fs/namespace.c:2870
SYSC_mount fs/namespace.c:3095 [inline]
SyS_mount+0xa8/0x120 fs/namespace.c:3072
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x44b5e9
RSP: 002b:00007f9b3a9d1d88 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000006ddc38 RCX: 000000000044b5e9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000000
RBP: 00000000006ddc30 R08: 0000000020000440 R09: 0000000000000000
R10: 0000000000000020 R11: 0000000000000246 R12: 000000005f671b56
R13: 000000005f671b56 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:

2 locks held by kworker/u4:1/22:

#0: ("writeback"){+.+.}, at: [<ffffffff81373630>] process_one_work+0x6b0/0x14a0 kernel/workqueue.c:2087
#1: ((&(&wb->dwork)->work)){+.+.}, at: [<ffffffff81373666>] process_one_work+0x6e6/0x14a0 kernel/workqueue.c:2091

1 lock held by khungtaskd/1530:

#0: (tasklist_lock){.+.+}, at: [<ffffffff81430dd4>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548

2 locks held by syz-executor694/8019:
#0: (&type->s_umount_key#47){+.+.}, at: [<ffffffff819092e7>] do_remount fs/namespace.c:2364 [inline]
#0: (&type->s_umount_key#47){+.+.}, at: [<ffffffff819092e7>] do_mount+0x837/0x2a00 fs/namespace.c:2870

#1: (&bdi->wb_switch_rwsem){+.+.}, at: [<ffffffff8192dfa6>] bdi_down_write_wb_switch_rwsem fs/fs-writeback.c:338 [inline]
#1: (&bdi->wb_switch_rwsem){+.+.}, at: [<ffffffff8192dfa6>] sync_inodes_sb+0x156/0x880 fs/fs-writeback.c:2469

=============================================

NMI backtrace for cpu 0

CPU: 0 PID: 1530 Comm: khungtaskd Not tainted 4.14.213-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x283 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x13a/0x17f lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5b9/0xb40 kernel/hung_task.c:274
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1

CPU: 1 PID: 8 Comm: rcu_preempt Not tainted 4.14.213-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

task: ffff8880b5414200 task.stack: ffff8880b5418000
RIP: 0010:lock_release+0x27/0x870 kernel/locking/lockdep.c:4007
RSP: 0018:ffff8880b541fa60 EFLAGS: 00000086
RAX: dffffc0000000000 RBX: 0000000000000086 RCX: ffffffff88f7fd40
RDX: ffffffff8321e8aa RSI: 0000000000000001 RDI: ffffffff8bfb09e0
RBP: ffffffff8bfb09e0 R08: ffffffff8b9ac430 R09: 0000000000000086
R10: ffff8880b5414ab0 R11: ffff8880b5414200 R12: ffffffff8321e8aa
R13: 1ffff11016a83f64 R14: ffff8880b541fd18 R15: ffffffff8bfb09c8
FS: 0000000000000000(0000) GS:ffff8880ba500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6e1df7d000 CR3: 00000000a1849000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:158 [inline]
_raw_spin_unlock_irqrestore+0x1b/0xe0 kernel/locking/spinlock.c:192
debug_object_deactivate lib/debugobjects.c:530 [inline]
debug_object_deactivate+0x1da/0x2e0 lib/debugobjects.c:491
debug_timer_deactivate kernel/time/timer.c:698 [inline]
debug_deactivate kernel/time/timer.c:750 [inline]
detach_timer kernel/time/timer.c:790 [inline]
detach_if_pending+0x82/0x430 kernel/time/timer.c:809
try_to_del_timer_sync+0x9a/0xe0 kernel/time/timer.c:1181
del_timer_sync+0x17c/0x240 kernel/time/timer.c:1246
schedule_timeout+0x4b7/0xe90 kernel/time/timer.c:1748
rcu_gp_kthread+0xc0a/0x1e60 kernel/rcu/tree.c:2255

kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Code: 0f 1f 40 00 48 b8 00 00 00 00 00 fc ff df 41 57 41 56 41 55 41 54 49 89 d4 55 48 89 fd 53 48 83 ec 58 48 c7 44 24 18 b3 8a b5 41 <48> 8d 5c 24 18 48 c7 44 24 20 74 5c b5 88 48 c1 eb 03 48 c7 44