INFO: task hung in __do_page_fault

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
18b7fd1c93e5204355ddbf2608a097d64df81b88 (Sat Apr 14 15:50:50 2018 +0000)
Merge branch 'akpm' (patches from Andrew)
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=ed2546e8398d45abf658

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=6127621175771136
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-8852471259444315113
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ed2546...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

CPU: 0 PID: 17444 Comm: syz-executor1 Not tainted 4.16.0+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1b9/0x294 lib/dump_stack.c:113
handle_userfault.cold.32+0x44/0x57 fs/userfaultfd.c:430
INFO: task kworker/0:0:30523 blocked for more than 120 seconds.
Not tainted 4.16.0+ #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/0:0 D
do_anonymous_page mm/memory.c:3147 [inline]
handle_pte_fault mm/memory.c:3961 [inline]
__handle_mm_fault+0x34be/0x4150 mm/memory.c:4087
23360 30523 2 0x80000000
Workqueue: events cgwb_release_workfn
handle_mm_fault+0x53a/0xc70 mm/memory.c:4124
Call Trace:
context_switch kernel/sched/core.c:2848 [inline]
__schedule+0x801/0x1e30 kernel/sched/core.c:3490
__do_page_fault+0x60b/0xe40 arch/x86/mm/fault.c:1399
do_page_fault+0xee/0x8a7 arch/x86/mm/fault.c:1474
page_fault+0x25/0x50 arch/x86/entry/entry_64.S:1159
RIP: 0010:copy_user_generic_unrolled+0x86/0xc0
arch/x86/lib/copy_user_64.S:65
RSP: 0018:ffff8801b57ffce8 EFLAGS: 00010206
RAX: ffffed0036afffae RBX: 0000000000000018 RCX: 0000000000000003
RDX: 0000000000000000 RSI: 0000000020013000 RDI: ffff8801b57ffd58
RBP: ffff8801b57ffd20 R08: ffffed0036afffae R09: ffffed0036afffab
R10: ffffed0036afffad R11: ffff8801b57ffd6f R12: 0000000020013018
R13: 0000000020013000 R14: ffff8801b57ffd58 R15: 00007ffffffff000
copy_from_user include/linux/uaccess.h:147 [inline]
SYSC_sigaltstack kernel/signal.c:3539 [inline]
SyS_sigaltstack+0xae/0x320 kernel/signal.c:3535
schedule+0xef/0x430 kernel/sched/core.c:3549
do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x455319
RSP: 002b:00007fe24ecf0c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000083
RAX: ffffffffffffffda RBX: 00007fe24ecf16d4 RCX: 0000000000455319
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000020013000
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000609 R14: 00000000006fc178 R15: 0000000000000000
FAULT_FLAG_ALLOW_RETRY missing 30
bit_wait+0x18/0x90 kernel/sched/wait_bit.c:197
__wait_on_bit+0xb3/0x130 kernel/sched/wait_bit.c:48
CPU: 0 PID: 17497 Comm: syz-executor1 Not tainted 4.16.0+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1b9/0x294 lib/dump_stack.c:113
out_of_line_wait_on_bit+0x204/0x3a0 kernel/sched/wait_bit.c:63
handle_userfault.cold.32+0x44/0x57 fs/userfaultfd.c:430
wait_on_bit include/linux/wait_bit.h:76 [inline]
wb_shutdown+0x370/0x470 mm/backing-dev.c:366
do_anonymous_page mm/memory.c:3147 [inline]
handle_pte_fault mm/memory.c:3961 [inline]
__handle_mm_fault+0x34be/0x4150 mm/memory.c:4087
cgwb_release_workfn+0x87/0x750 mm/backing-dev.c:509
handle_mm_fault+0x53a/0xc70 mm/memory.c:4124
process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
__do_page_fault+0x60b/0xe40 arch/x86/mm/fault.c:1399
do_page_fault+0xee/0x8a7 arch/x86/mm/fault.c:1474
page_fault+0x25/0x50 arch/x86/entry/entry_64.S:1159
RIP: 0010:copy_user_generic_unrolled+0x86/0xc0
arch/x86/lib/copy_user_64.S:65
RSP: 0018:ffff8801b7947ce8 EFLAGS: 00010206
RAX: ffffed0036f28fae RBX: 0000000000000018 RCX: 0000000000000003
RDX: 0000000000000000 RSI: 0000000020013000 RDI: ffff8801b7947d58
RBP: ffff8801b7947d20 R08: ffffed0036f28fae R09: ffffed0036f28fab
R10: ffffed0036f28fad R11: ffff8801b7947d6f R12: 0000000020013018
R13: 0000000020013000 R14: ffff8801b7947d58 R15: 00007ffffffff000
copy_from_user include/linux/uaccess.h:147 [inline]
SYSC_sigaltstack kernel/signal.c:3539 [inline]
SyS_sigaltstack+0xae/0x320 kernel/signal.c:3535
do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x455319
RSP: 002b:00007fe24eccfc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000083
RAX: ffffffffffffffda RBX: 00007fe24ecd06d4 RCX: 0000000000455319
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000020013000
RBP: 000000000072bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000609 R14: 00000000006fc178 R15: 0000000000000001
worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
kthread+0x345/0x410 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411

Showing all locks held in the system:
2 locks held by khungtaskd/888:
#0: 00000000b28f14ec (rcu_read_lock){....}, at:
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: 00000000b28f14ec (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60
kernel/hung_task.c:249
#1: 00000000d6bbe5a4 (tasklist_lock){.+.+}, at:
debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
2 locks held by getty/4460:
#0: 00000000e22884b3 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000013ddc9b8 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4461:
#0: 000000005f04ec02 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000005d4f8527 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4462:
#0: 000000003405dd15 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000c3ec63c1 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4463:
#0: 00000000ec641df5 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000058ea1741 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4464:
#0: 00000000f097c053 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000c124b7ae (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4465:
#0: 00000000f89440e2 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000f6071068 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by kworker/0:0/30523:
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at:
__write_once_size include/linux/compiler.h:215 [inline]
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at: atomic64_set
include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at: atomic_long_set
include/asm-generic/atomic-long.h:57 [inline]
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at: set_work_data
kernel/workqueue.c:617 [inline]
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 00000000ffece5e8 ((wq_completion)"events"){+.+.}, at:
process_one_work+0xaef/0x1b50 kernel/workqueue.c:2116
#1: 00000000fdef1b4a ((work_completion)(&wb->release_work)){+.+.}, at:
process_one_work+0xb46/0x1b50 kernel/workqueue.c:2120
2 locks held by getty/12970:
#0: 000000001b7411ee (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000008730ecb6 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131

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

NMI backtrace for cpu 1
CPU: 1 PID: 888 Comm: khungtaskd Not tainted 4.16.0+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1b9/0x294 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
check_hung_task kernel/hung_task.c:132 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
watchdog+0xc10/0xf60 kernel/hung_task.c:249
kthread+0x345/0x410 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10
arch/x86/include/asm/irqflags.h:54


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