INFO: task hung in nmi_cpu_backtrace

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fc36def997cf mm: teach dump_page() to correctly output poi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15218058400000
kernel config: https://syzkaller.appspot.com/x/.config?x=f62553dc846b0692
dashboard link: https://syzkaller.appspot.com/bug?extid=86b9f1a1cf3db69d0855
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk]

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+86b9f1...@syzkaller.appspotmail.com

kworker/dying (276) used greatest stack depth: 12776 bytes left
INFO: task syz-executor4:18981 blocked for more than 120 seconds.
Not tainted 4.18.0-rc3+ #33
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

Showing all locks held in the system:
2 locks held by kworker/0:1/25:
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
__write_once_size include/linux/compiler.h:215 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at: atomic64_set
include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at: atomic_long_set
include/asm-generic/atomic-long.h:59 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at: set_work_data
kernel/workqueue.c:617 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
process_one_work+0xb44/0x1ba0 kernel/workqueue.c:2124
#1: 0000000092303d3f ((work_completion)(&smc->tcp_listen_work)){+.+.}, at:
process_one_work+0xb9b/0x1ba0 kernel/workqueue.c:2128
2 locks held by kworker/1:1/27:
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
__write_once_size include/linux/compiler.h:215 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at: atomic64_set
include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at: atomic_long_set
include/asm-generic/atomic-long.h:59 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at: set_work_data
kernel/workqueue.c:617 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 000000008e2cce76 ((wq_completion)"events"){+.+.}, at:
process_one_work+0xb44/0x1ba0 kernel/workqueue.c:2124
#1: 00000000c4e0dde8 ((work_completion)(&smc->tcp_listen_work)){+.+.}, at:
process_one_work+0xb9b/0x1ba0 kernel/workqueue.c:2128
1 lock held by khungtaskd/900:
#0: 00000000cd17448c (rcu_read_lock){....}, at:
debug_show_all_locks+0xd0/0x428 kernel/locking/lockdep.c:4461
1 lock held by rsyslogd/4435:
#0: 000000002864294e (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1bb/0x200
fs/file.c:766
2 locks held by getty/4525:
#0: 00000000d66ea930 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000dbde5f75 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/4526:
#0: 0000000017cee0aa (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000b6a820b2 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/4527:
#0: 00000000efb7d997 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000b17a4b7c (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/4528:
#0: 00000000cc67ad89 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000055ae238c (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/4529:
#0: 000000000f527055 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000009ffd58ec (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/4530:
#0: 00000000fcb739b2 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000007ea95d27 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/4531:
#0: 000000000c668fd5 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000007e6064af (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140

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

NMI backtrace for cpu 0
CPU: 0 PID: 900 Comm: khungtaskd Not tainted 4.18.0-rc3+ #33
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+0x1c9/0x2b4 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_uninterruptible_tasks kernel/hung_task.c:196 [inline]
watchdog+0x9c4/0xf80 kernel/hung_task.c:252
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10
arch/x86/include/asm/irqflags.h:54


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.