INFO: task hung in perf_event_free_task

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c6dd78fc Merge branch 'x86-urgent-for-linus' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10b33b58600000
kernel config: https://syzkaller.appspot.com/x/.config?x=7937b718ddac333b
dashboard link: https://syzkaller.appspot.com/bug?extid=7692cea7450c97fa2a0a
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e888cc600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7692ce...@syzkaller.appspotmail.com

INFO: task syz-executor.0:9658 blocked for more than 143 seconds.
Not tainted 5.2.0+ #37
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.0 D25992 9658 7837 0x00004006
Call Trace:
context_switch kernel/sched/core.c:3254 [inline]
__schedule+0x8b7/0xcd0 kernel/sched/core.c:3880
schedule+0x12f/0x1d0 kernel/sched/core.c:3944
perf_event_free_task+0x52a/0x630 kernel/events/core.c:11606
copy_process+0x39bb/0x5a00 kernel/fork.c:2283
_do_fork+0x179/0x630 kernel/fork.c:2369
__do_sys_clone kernel/fork.c:2524 [inline]
__se_sys_clone kernel/fork.c:2505 [inline]
__x64_sys_clone+0x247/0x2b0 kernel/fork.c:2505
do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459829
Code: dd fe ff ff cc cc cc cc cc cc cc cc cc cc cc cc cc 64 48 8b 0c 25 f8
ff ff ff 48 3b 61 10 76 68 48 83 ec 28 48 89 6c 24 20 48 <8d> 6c 24 20 48
8b 44 24 30 48 89 04 24 48 8b 4c 24 38 48 89 4c 24
RSP: 002b:00007f2b371d8c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000459829
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000002102001ffe
RBP: 000000000075bf20 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2b371d96d4
R13: 00000000004bfce6 R14: 00000000004d17f8 R15: 00000000ffffffff

Showing all locks held in the system:
1 lock held by khungtaskd/1056:
#0: 000000004ef21d86 (rcu_read_lock){....}, at: rcu_lock_acquire+0x4/0x30
include/linux/rcupdate.h:207
1 lock held by rsyslogd/7708:
#0: 000000001dbc8cee (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x243/0x2e0
fs/file.c:801
2 locks held by getty/7798:
#0: 00000000ad2eb6b3 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 0000000067bda1b9 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7799:
#0: 00000000e86f0102 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 00000000f10c3522 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7800:
#0: 00000000f4a9ed02 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 00000000759669da (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7801:
#0: 00000000c998e0d2 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 000000007c9ea7de (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7802:
#0: 00000000398be820 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 00000000deef3632 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7803:
#0: 00000000fa979d44 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 000000003715a25d (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7804:
#0: 000000009d01c162 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 0000000010022d29 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156

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

NMI backtrace for cpu 0
CPU: 0 PID: 1056 Comm: khungtaskd Not tainted 5.2.0+ #37
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+0x1d8/0x2f8 lib/dump_stack.c:113
nmi_cpu_backtrace+0xb0/0x1a0 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x14c/0x240 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xbcc/0xbe0 kernel/hung_task.c:289
kthread+0x332/0x350 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0xe/0x10
arch/x86/include/asm/irqflags.h:60


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[syzbot]

syzbot has bisected this bug to:

commit 1cf8dfe8a661f0462925df943140e9f6d1ea5233
Author: Peter Zijlstra <pet...@infradead.org>
Date: Sat Jul 13 09:21:25 2019 +0000

perf/core: Fix race between close() and fork()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1523f40c600000
start commit: c6dd78fc Merge branch 'x86-urgent-for-linus' of git://git...
git tree: upstream
final crash: https://syzkaller.appspot.com/x/report.txt?x=1723f40c600000
console output: https://syzkaller.appspot.com/x/log.txt?x=1323f40c600000

kernel config: https://syzkaller.appspot.com/x/.config?x=7937b718ddac333b
dashboard link: https://syzkaller.appspot.com/bug?extid=7692cea7450c97fa2a0a

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e888cc600000

Reported-by: syzbot+7692ce...@syzkaller.appspotmail.com
Fixes: 1cf8dfe8a661 ("perf/core: Fix race between close() and fork()")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 7af08140 Revert "gcov: clang: fix clang-11+ build"
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15416871d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c0a6882014fd3d45
dashboard link: https://syzkaller.appspot.com/bug?extid=7692cea7450c97fa2a0a
compiler: Debian clang version 11.0.1-2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=145c9ffed00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12de31ded00000

The issue was bisected to:

commit 1cf8dfe8a661f0462925df943140e9f6d1ea5233
Author: Peter Zijlstra <pet...@infradead.org>
Date: Sat Jul 13 09:21:25 2019 +0000

perf/core: Fix race between close() and fork()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1523f40c600000

final oops: https://syzkaller.appspot.com/x/report.txt?x=1723f40c600000
console output: https://syzkaller.appspot.com/x/log.txt?x=1323f40c600000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7692ce...@syzkaller.appspotmail.com

Fixes: 1cf8dfe8a661 ("perf/core: Fix race between close() and fork()")

INFO: task syz-executor890:6628 blocked for more than 143 seconds.
Not tainted 5.12.0-rc8-syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:syz-executor890 state:D stack:25968 pid: 6628 ppid: 8391 flags:0x00004004
Call Trace:
context_switch kernel/sched/core.c:4322 [inline]
__schedule+0xa4d/0xf80 kernel/sched/core.c:5073
schedule+0x14b/0x200 kernel/sched/core.c:5152
perf_event_free_task+0x575/0x6a0 kernel/events/core.c:12623
copy_process+0x418f/0x57e0 kernel/fork.c:2376
kernel_clone+0x21a/0x7d0 kernel/fork.c:2500
__do_sys_clone kernel/fork.c:2617 [inline]
__se_sys_clone kernel/fork.c:2601 [inline]
__x64_sys_clone+0x236/0x2b0 kernel/fork.c:2601
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x44b6e9
RSP: 002b:00007fd6c1512208 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00000000004d7288 RCX: 000000000044b6e9
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000022086605
RBP: 00000000004d7280 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004d728c
R13: 00007ffc3bab65ef R14: 00007fd6c1512300 R15: 0000000000022000

Showing all locks held in the system:

1 lock held by khungtaskd/1623:
#0: ffffffff8cd10280 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30 arch/x86/pci/mmconfig_64.c:151
2 locks held by systemd-journal/4819:
1 lock held by in:imklog/8079:
#0: ffff8880163265f0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x24e/0x2f0 fs/file.c:974
2 locks held by syz-executor890/6495:

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

NMI backtrace for cpu 1
CPU: 1 PID: 1623 Comm: khungtaskd Not tainted 5.12.0-rc8-syzkaller #0

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

__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x202/0x31e lib/dump_stack.c:120
nmi_cpu_backtrace+0x16c/0x190 lib/nmi_backtrace.c:105
nmi_trigger_cpumask_backtrace+0x191/0x2f0 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:209 [inline]
watchdog+0xcfb/0xd40 kernel/hung_task.c:294
kthread+0x39a/0x3c0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Sending NMI from CPU 1 to CPUs 0:

NMI backtrace for cpu 0

CPU: 0 PID: 6495 Comm: syz-executor890 Not tainted 5.12.0-rc8-syzkaller #0

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

RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:155 [inline]
RIP: 0010:unwind_next_frame+0x184/0x1f90 arch/x86/kernel/unwind_orc.c:443
Code: 89 7c 24 70 0f 84 1a 01 00 00 48 c7 c0 00 00 00 81 49 39 c4 0f 82 16 01 00 00 48 c7 c0 52 83 e0 89 49 39 c4 0f 83 06 01 00 00 <48> c7 c0 00 00 00 81 4c 89 e5 48 29 c5 48 c1 ed 08 48 c7 c0 e8 8d
RSP: 0000:ffffc9000dd5f720 EFLAGS: 00000087
RAX: ffffffff89e08352 RBX: ffffc9000dd5f828 RCX: ffffffff9031ab03
RDX: ffffc9000dd5fc20 RSI: ffffffff814e6de0 RDI: 0000000000000001
RBP: ffffc9000dd5f815 R08: 0000000000000003 R09: ffffc9000dd5f8b0
R10: fffff52001babf08 R11: 0000000000000000 R12: ffffffff814e6ddf
R13: ffffc9000dd5f7e0 R14: dffffc0000000000 R15: 1ffff92001babf02
FS: 00007fd6c1512700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000022000 CR3: 0000000034d8b000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
arch_stack_walk+0xb2/0xe0 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x104/0x1e0 kernel/stacktrace.c:121
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:427 [inline]
__kasan_slab_alloc+0x8f/0xc0 mm/kasan/common.c:460
kasan_slab_alloc include/linux/kasan.h:223 [inline]
slab_post_alloc_hook mm/slab.h:516 [inline]
slab_alloc_node mm/slub.c:2907 [inline]
slab_alloc mm/slub.c:2915 [inline]
kmem_cache_alloc+0x1c3/0x350 mm/slub.c:2920
__sigqueue_alloc+0x2c2/0x490 kernel/signal.c:435
__send_signal+0x210/0xe50 kernel/signal.c:1116
force_sig_info_to_task+0x2a4/0x3f0 kernel/signal.c:1334
force_sig_fault_to_task kernel/signal.c:1673 [inline]
force_sig_fault+0x11e/0x1c0 kernel/signal.c:1680
__bad_area_nosemaphore+0x390/0x570 arch/x86/mm/fault.c:840
handle_page_fault arch/x86/mm/fault.c:1475 [inline]
exc_page_fault+0xa1/0x1e0 arch/x86/mm/fault.c:1531
asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577
RIP: 0033:0x22000
Code: Unable to access opcode bytes at RIP 0x21fd6.
RSP: 002b:00007fd6c1512220 EFLAGS: 00010206
RAX: ffffffffffffffff RBX: 00000000004d7288 RCX: ffffffffffffffbc
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000000
RBP: 00000000004d7280 R08: 0000000000000000 R09: 00007fd6c1512300
R10: 00000000ffffffff R11: 0000000000000246 R12: 00000000004d728c
R13: 00007ffc3bab65ef R14: 00007fd6c1512300 R15: 0000000000022000

[Peter Zijlstra]

On Tue, Apr 20, 2021 at 02:10:22AM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 7af08140 Revert "gcov: clang: fix clang-11+ build"
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15416871d00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=c0a6882014fd3d45
> dashboard link: https://syzkaller.appspot.com/bug?extid=7692cea7450c97fa2a0a
> compiler: Debian clang version 11.0.1-2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=145c9ffed00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12de31ded00000

When I build that C file and run it, it completes. AFAICT that's not the
expected outcome given we're looking for a hung-task scenario. Hmm?

[Dmitry Vyukov]

I just reproduced it on some similar kernel I had. Maybe you used a
different config. Or maybe it requires a similar qemu machine.
However, the reproducer looks like a fork bomb and it produced
thousands of subprocesses and took some time.
In the past 2 years it's been happening all reproducers look similar
and involve clone and perf_event_open.



INFO: task a.out:13194 blocked for more than 143 seconds.
Not tainted 5.12.0-rc5-next-20210330 #113

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:a.out state:D stack:28616 pid:13194 ppid: 23696 flags:0x00004004
Call Trace:
context_switch kernel/sched/core.c:4329 [inline]
__schedule+0x911/0x2160 kernel/sched/core.c:5079
schedule+0xcf/0x270 kernel/sched/core.c:5158
perf_event_free_task+0x519/0x6c0 kernel/events/core.c:12627
copy_process+0x4a1e/0x70b0 kernel/fork.c:2377
kernel_clone+0xe7/0xab0 kernel/fork.c:2501
__do_sys_clone+0xc8/0x110 kernel/fork.c:2618
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x451e49
RSP: 002b:00007fa8e0d66118 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000451e49

RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000022086605

RBP: 00007fa8e0d66200 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc688a6c7e
R13: 00007ffc688a6c7f R14: 00007fa8e0d66300 R15: 0000000000022000

Showing all locks held in the system:

3 locks held by kworker/u8:1/35:
#0: ffff888010782938 ((wq_completion)netns){+.+.}-{0:0}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff888010782938 ((wq_completion)netns){+.+.}-{0:0}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff888010782938 ((wq_completion)netns){+.+.}-{0:0}, at:
atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff888010782938 ((wq_completion)netns){+.+.}-{0:0}, at:
set_work_data kernel/workqueue.c:616 [inline]
#0: ffff888010782938 ((wq_completion)netns){+.+.}-{0:0}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
#0: ffff888010782938 ((wq_completion)netns){+.+.}-{0:0}, at:
process_one_work+0x871/0x1600 kernel/workqueue.c:2246
#1: ffffc90000597da8 (net_cleanup_work){+.+.}-{0:0}, at:
process_one_work+0x8a5/0x1600 kernel/workqueue.c:2250
#2: ffffffff8ce94f50 (pernet_ops_rwsem){++++}-{3:3}, at:
cleanup_net+0x9b/0xb10 net/core/net_namespace.c:557
3 locks held by kworker/u8:3/269:
1 lock held by khungtaskd/1654:
#0: ffffffff8b7773a0 (rcu_read_lock){....}-{1:2}, at:
debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6333
1 lock held by rsyslogd/8425:
#0: ffff88801433edf0 (&f->f_pos_lock){+.+.}-{3:3}, at:
__fdget_pos+0xe9/0x100 fs/file.c:967
2 locks held by getty/8519:
#0: ffff888020a09098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc9000115b2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178
2 locks held by getty/8520:
#0: ffff888025793098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc9000113b2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178
2 locks held by getty/8521:
#0: ffff8880194b5098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc900011ab2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178
2 locks held by getty/8522:
#0: ffff888020a0f098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc900011db2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178
2 locks held by getty/8523:
#0: ffff888019293098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc900011bb2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178
2 locks held by getty/8524:
#0: ffff888019296098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc900011cb2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178
2 locks held by kworker/0:5/8616:
#0: ffff88800fc64d38 ((wq_completion)events){+.+.}-{0:0}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff88800fc64d38 ((wq_completion)events){+.+.}-{0:0}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff88800fc64d38 ((wq_completion)events){+.+.}-{0:0}, at:
atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff88800fc64d38 ((wq_completion)events){+.+.}-{0:0}, at:
set_work_data kernel/workqueue.c:616 [inline]
#0: ffff88800fc64d38 ((wq_completion)events){+.+.}-{0:0}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
#0: ffff88800fc64d38 ((wq_completion)events){+.+.}-{0:0}, at:
process_one_work+0x871/0x1600 kernel/workqueue.c:2246
#1: ffffc90001d77da8 ((kfence_timer).work){+.+.}-{0:0}, at:
process_one_work+0x8a5/0x1600 kernel/workqueue.c:2250
2 locks held by bash/13876:
#0: ffff88804e222098 (&tty->ldisc_sem){++++}-{0:0}, at:
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:266
#1: ffffc9000be332e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
n_tty_read+0xd5b/0x12f0 drivers/tty/n_tty.c:2178

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

NMI backtrace for cpu 3
CPU: 3 PID: 1654 Comm: khungtaskd Not tainted 5.12.0-rc5-next-20210330 #113
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.13.0-44-g88ab0c15525c-prebuilt.qemu.org 04/01/2014

Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]

dump_stack+0x141/0x1d7 lib/dump_stack.c:120
nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:253 [inline]
watchdog+0xd8e/0xf40 kernel/hung_task.c:338
kthread+0x3b1/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Sending NMI from CPU 3 to CPUs 0-2:
NMI backtrace for cpu 2 skipped: idling at native_safe_halt
arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 2 skipped: idling at arch_safe_halt
arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 2 skipped: idling at default_idle+0xe/0x10
arch/x86/kernel/process.c:683
NMI backtrace for cpu 0 skipped: idling at native_safe_halt
arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt
arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0xe/0x10
arch/x86/kernel/process.c:683
NMI backtrace for cpu 1 skipped: idling at native_safe_halt
arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt
arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0xe/0x10
arch/x86/kernel/process.c:683

[Dmitry Vyukov]

Interestingly this reproduced with the simpler syzkaller reproducer in
~30 seconds and w/o creating fork bomb (at least I looked at the
number of processes initially and it did not jump to thousands). So
maybe the fork bomb is just a red herring.

cat /tmp/prog
perf_event_open(&(0x7f0000940000)={0x2, 0x70, 0xee6a, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_config_ext}, 0x0, 0x0,
0xffffffffffffffff, 0x0)
clone(0x2102001ffe, 0x0, 0xfffffffffffffffe, 0x0, 0xffffffffffffffff)
ioctl$PERF_EVENT_IOC_RESET(0xffffffffffffffff, 0x2403, 0x0)

./syz-execprog -repeat=0 -procs=4 prog

2021/04/21 12:19:31 executed programs: 2986
2021/04/21 12:19:36 executed programs: 3667
2021/04/21 12:19:41 executed programs: 4323
[ 254.362146][ T3344] ieee802154 phy0 wpan0: encryption failed: -22
[ 254.363064][ T3344] ieee802154 phy1 wpan1: encryption failed: -22
2021/04/21 12:19:46 executed programs: 4984
2021/04/21 12:19:51 executed programs: 5649
[ 315.807468][ T3344] ieee802154 phy0 wpan0: encryption failed: -22
[ 315.809063][ T3344] ieee802154 phy1 wpan1: encryption failed: -22
[ 328.121848][ T25] Bluetooth: hci4: command 0x0406 tx timeout
[ 328.121849][ T8706] Bluetooth: hci1: command 0x0406 tx timeout
[ 328.121931][ T8706] Bluetooth: hci3: command 0x0406 tx timeout
[ 328.123555][ T25] Bluetooth: hci2: command 0x0406 tx timeout
[ 328.128087][ T25] Bluetooth: hci5: command 0x0406 tx timeout
[ 338.371924][ T2997] Bluetooth: hci0: command 0x0406 tx timeout
[ 339.471747][ T1294] unregister_netdevice: waiting for ip6gre0 to
become free. Usage count = 2

Message from syslogd@syzkaller at Apr 21 12:21:10 ...
kernel:[ 339.471747][ T1294] unregister_netdevice: waiting for
ip6gre0 to become free. Usage count = 2
[ 377.242537][ T3344] ieee802154 phy0 wpan0: encryption failed: -22
[ 377.243562][ T3344] ieee802154 phy1 wpan1: encryption failed: -22
[ 406.042164][ T1651] INFO: task syz-executor:10479 can't die for
more than 143 seconds.
[ 406.045360][ T1651] task:syz-executor state:D stack:28904
pid:10479 ppid: 11138 flags:0x00004006
[ 406.048146][ T1651] Call Trace:
[ 406.049143][ T1651] __schedule+0x911/0x2160
[ 406.050531][ T1651] ? io_schedule_timeout+0x140/0x140
[ 406.053016][ T1651] ? prepare_to_wait_event+0x129/0x7e0
[ 406.053825][ T1651] schedule+0xcf/0x270
[ 406.054373][ T1651] perf_event_free_task+0x519/0x6c0
[ 406.055117][ T1651] ? perf_event_exit_task+0xf10/0xf10
[ 406.055890][ T1651] ? init_wait_var_entry+0x200/0x200
[ 406.056657][ T1651] copy_process+0x4a1e/0x70b0
[ 406.057320][ T1651] ? mark_lock+0xef/0x17b0
[ 406.057952][ T1651] ? __cleanup_sighand+0xb0/0xb0
[ 406.058658][ T1651] ? do_futex+0x165/0x1780
[ 406.059283][ T1651] ? __lock_acquire+0x16a7/0x5230
[ 406.060002][ T1651] ? kernel_clone+0x314/0xab0
[ 406.060663][ T1651] kernel_clone+0xe7/0xab0
[ 406.061289][ T1651] ? create_io_thread+0xf0/0xf0
[ 406.062930][ T1651] ? lockdep_hardirqs_on_prepare+0x400/0x400
[ 406.063908][ T1651] ? __sanitizer_cov_trace_const_cmp4+0x1c/0x70
[ 406.064806][ T1651] ? find_held_lock+0x2d/0x110
[ 406.065491][ T1651] __do_sys_clone+0xc8/0x110
[ 406.066154][ T1651] ? kernel_clone+0xab0/0xab0
[ 406.066828][ T1651] ? __context_tracking_enter+0xef/0x100
[ 406.067649][ T1651] ? syscall_enter_from_user_mode+0x27/0x70
[ 406.068493][ T1651] do_syscall_64+0x2d/0x70
[ 406.069125][ T1651] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 406.069980][ T1651] RIP: 0033:0x465f69
[ 406.070545][ T1651] RSP: 002b:00007f6178513188 EFLAGS: 00000246
ORIG_RAX: 0000000000000038
[ 406.073140][ T1651] RAX: ffffffffffffffda RBX: 000000000056bf60
RCX: 0000000000465f69
[ 406.074357][ T1651] RDX: 9999999999999999 RSI: 0000000000000000
RDI: 0000002102001ffe
[ 406.075488][ T1651] RBP: 00000000004bfa8f R08: ffffffffffffffff
R09: 0000000000000000
[ 406.076597][ T1651] R10: 0000000000000000 R11: 0000000000000246
R12: 000000000056bf60
[ 406.077706][ T1651] R13: 00007ffcf37755cf R14: 00007f6178513300
R15: 0000000000022000
[ 406.078886][ T1651] INFO: task syz-executor:10479 blocked for more
than 143 seconds.
[ 406.079983][ T1651] Not tainted 5.12.0-rc5-next-20210330 #113
[ 406.080880][ T1651] "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 406.082994][ T1651] task:syz-executor state:D stack:28904
pid:10479 ppid: 11138 flags:0x00004006
[ 406.084212][ T1651] Call Trace:
[ 406.084638][ T1651] __schedule+0x911/0x2160
[ 406.085191][ T1651] ? io_schedule_timeout+0x140/0x140
[ 406.085887][ T1651] ? prepare_to_wait_event+0x129/0x7e0
[ 406.086566][ T1651] schedule+0xcf/0x270
[ 406.087080][ T1651] perf_event_free_task+0x519/0x6c0
[ 406.087727][ T1651] ? perf_event_exit_task+0xf10/0xf10
[ 406.088387][ T1651] ? init_wait_var_entry+0x200/0x200
[ 406.089081][ T1651] copy_process+0x4a1e/0x70b0
[ 406.089659][ T1651] ? mark_lock+0xef/0x17b0
[ 406.090214][ T1651] ? __cleanup_sighand+0xb0/0xb0
[ 406.090836][ T1651] ? do_futex+0x165/0x1780
[ 406.091448][ T1651] ? __lock_acquire+0x16a7/0x5230
[ 406.092296][ T1651] ? kernel_clone+0x314/0xab0
[ 406.093006][ T1651] kernel_clone+0xe7/0xab0
[ 406.093688][ T1651] ? create_io_thread+0xf0/0xf0
[ 406.094357][ T1651] ? lockdep_hardirqs_on_prepare+0x400/0x400
[ 406.095348][ T1651] ? __sanitizer_cov_trace_const_cmp4+0x1c/0x70
[ 406.096633][ T1651] ? find_held_lock+0x2d/0x110
[ 406.097618][ T1651] __do_sys_clone+0xc8/0x110
[ 406.098563][ T1651] ? kernel_clone+0xab0/0xab0
[ 406.099531][ T1651] ? __context_tracking_enter+0xef/0x100
[ 406.100832][ T1651] ? syscall_enter_from_user_mode+0x27/0x70
[ 406.102608][ T1651] do_syscall_64+0x2d/0x70
[ 406.103320][ T1651] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 406.104220][ T1651] RIP: 0033:0x465f69
[ 406.104758][ T1651] RSP: 002b:00007f6178513188 EFLAGS: 00000246
ORIG_RAX: 0000000000000038
[ 406.105898][ T1651] RAX: ffffffffffffffda RBX: 000000000056bf60
RCX: 0000000000465f69
[ 406.106978][ T1651] RDX: 9999999999999999 RSI: 0000000000000000
RDI: 0000002102001ffe
[ 406.108023][ T1651] RBP: 00000000004bfa8f R08: ffffffffffffffff
R09: 0000000000000000
[ 406.108973][ T1651] R10: 0000000000000000 R11: 0000000000000246
R12: 000000000056bf60
[ 406.109924][ T1651] R13: 00007ffcf37755cf R14: 00007f6178513300
R15: 0000000000022000
[ 406.110908][ T1651]
[ 406.110908][ T1651] Showing all locks held in the system:
[ 406.111863][ T1651] 2 locks held by kworker/u8:3/278:
[ 406.112494][ T1651] 3 locks held by kworker/u8:5/1294:
[ 406.113133][ T1651] #0: ffff888010782938

((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x871/0x1600

[ 406.114459][ T1651] #1: ffffc90004f17da8

(net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x8a5/0x1600

[ 406.115681][ T1651] #2: ffffffff8ce94f50

(pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x9b/0xb10

[ 406.116838][ T1651] 1 lock held by khungtaskd/1651:
[ 406.117488][ T1651] #0: ffffffff8b7773a0

(rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260

[ 406.118866][ T1651] 4 locks held by rs:main Q:Reg/8514:
[ 406.119589][ T1651] 1 lock held by rsyslogd/8516:
[ 406.120237][ T1651] #0: ffff888019411770

(&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100

[ 406.121488][ T1651] 2 locks held by getty/8614:
[ 406.122287][ T1651] #0: ffff8880153e3098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.123642][ T1651] #1: ffffc90000f7f2e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.125102][ T1651] 2 locks held by getty/8615:
[ 406.125734][ T1651] #0: ffff888029bfd098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.127074][ T1651] #1: ffffc90000f872e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.128470][ T1651] 2 locks held by getty/8616:
[ 406.129104][ T1651] #0: ffff8880197b3098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.130444][ T1651] #1: ffffc90000fbb2e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.132580][ T1651] 2 locks held by getty/8617:
[ 406.133214][ T1651] #0: ffff888029bff098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.134601][ T1651] #1: ffffc90000f7b2e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.135977][ T1651] 2 locks held by getty/8618:
[ 406.136626][ T1651] #0: ffff88801438c098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.137949][ T1651] #1: ffffc90000feb2e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.139321][ T1651] 2 locks held by getty/8619:
[ 406.139949][ T1651] #0: ffff8880197b2098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.141291][ T1651] #1: ffffc90000ffb2e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.142713][ T1651] 2 locks held by bash/8632:
[ 406.143342][ T1651] #0: ffff888026ead098

(&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80

[ 406.144751][ T1651] #1: ffffc9000102b2e8

(&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xd5b/0x12f0

[ 406.146158][ T1651]
[ 406.146476][ T1651] =============================================
[ 406.146476][ T1651]
[ 406.147615][ T1651] NMI backtrace for cpu 0
[ 406.148204][ T1651] CPU: 0 PID: 1651 Comm: khungtaskd Not tainted
5.12.0-rc5-next-20210330 #113
[ 406.149397][ T1651] Hardware name: QEMU Standard PC (Q35 + ICH9,
2009), BIOS rel-1.13.0-44-g88ab0c15525c-prebuilt.qemu.org 04/01/2014
[ 406.151034][ T1651] Call Trace:
[ 406.151479][ T1651] dump_stack+0x141/0x1d7
[ 406.152081][ T1651] nmi_cpu_backtrace.cold+0x44/0xd7
[ 406.152792][ T1651] ? lapic_can_unplug_cpu+0x80/0x80
[ 406.153500][ T1651] nmi_trigger_cpumask_backtrace+0x1b3/0x230
[ 406.154378][ T1651] watchdog+0xd8e/0xf40
[ 406.154957][ T1651] ? trace_sched_process_hang+0x280/0x280
[ 406.155763][ T1651] kthread+0x3b1/0x4a0
[ 406.156321][ T1651] ? __kthread_bind_mask+0xc0/0xc0
[ 406.157029][ T1651] ret_from_fork+0x1f/0x30
[ 406.157689][ T1651] Sending NMI from CPU 0 to CPUs 1-3:
[ 406.158579][ C2] NMI backtrace for cpu 2 skipped: idling at
default_idle+0xe/0x10
[ 406.158601][ C1] NMI backtrace for cpu 1 skipped: idling at
default_idle+0xe/0x10
[ 406.159131][ C3] NMI backtrace for cpu 3
[ 406.159144][ C3] CPU: 3 PID: 8514 Comm: rs:main Q:Reg Not
tainted 5.12.0-rc5-next-20210330 #113
[ 406.159156][ C3] Hardware name: QEMU Standard PC (Q35 + ICH9,
2009), BIOS rel-1.13.0-44-g88ab0c15525c-prebuilt.qemu.org 04/01/2014
[ 406.159169][ C3] RIP: 0010:__sanitizer_cov_trace_pc+0x7/0x60
[.159182]
0 00 4d CMeossdagee :fr omf sfy ffsl ogbd@9sy zkfalfle r ff fatf A prf
2f1 1b2:a2 2:08 0170 . ..0
8b 03 48 k er0nefl: [ b 4d06 .1ca 459961 3]8[ bT1 6541]5 K 00 er4ne8l
pa6ni3c - cno9 e9t sy6nc4in g:f hfun g_ff ftafsk : 0blfoc ke1d fta
40 sk0s0 65 8b 0
8e 7e <89> c1 48 8b 34 24 81 e1 00 01 00 00 65 48 8b 14 25 00 f0 01 00 a9
[ 406.159200][ C3] RSP: 0018:ffffc90001467848 EFLAGS: 00000246
[ 406.159214][ C3] RAX: 0000000080000000 RBX: 000000000000000e
RCX: 0000000000000000
[ 406.159225][ C3] RDX: 0000000000000000 RSI: ffff888012a8c700
RDI: 0000000000000003
[ 406.159235][ C3] RBP: 0000000000000000 R08: 0000000000000000
R09: 0000000000000000
[ 406.159244][ C3] R10: ffffffff8197f862 R11: 0000000000000000
R12: ffffea00008fc840
[ 406.159255][ C3] R13: dffffc0000000000 R14: 0000000000000000
R15: ffffea00008fc840
[ 406.159265][ C3] FS: 00007f98afbad700(0000)
GS:ffff88802d180000(0000) knlGS:0000000000000000
[ 406.159275][ C3] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 406.159284][ C3] CR2: ffffffffff600400 CR3: 0000000014c6d000
CR4: 0000000000750ee0
[ 406.159294][ C3] DR0: 0000000000000000 DR1: 0000000000000000
DR2: 0000000000000000
[ 406.159304][ C3] DR3: 0000000000000000 DR6: 00000000fffe0ff0
DR7: 0000000000000400
[ 406.159312][ C3] PKRU: 55555554
[ 406.159317][ C3] Call Trace:
[ 406.159322][ C3] pagecache_get_page+0xa0c/0x18d0
[ 406.159329][ C3] ? add_to_page_cache_lru+0x5b0/0x5b0
[ 406.159337][ C3] grab_cache_page_write_begin+0x64/0x90
[ 406.159344][ C3] ext4_da_write_begin+0x35c/0x1160
[ 406.159351][ C3] ? ktime_get_coarse_real_ts64+0x1b7/0x200
[ 406.159359][ C3] ? __sanitizer_cov_trace_const_cmp8+0x1d/0x70
[ 406.159366][ C3] ? ext4_write_begin+0x14b0/0x14b0
[ 406.159373][ C3] ? copyout_mc+0x110/0x110
[ 406.159380][ C3] ? __sanitizer_cov_trace_const_cmp4+0x1c/0x70
[ 406.159387][ C3] ? current_time+0x220/0x2c0
[ 406.159393][ C3] generic_perform_write+0x20a/0x4f0
[ 406.159400][ C3] ? generic_file_readonly_mmap+0x1b0/0x1b0
[ 406.159408][ C3] ? down_write_killable+0x170/0x170
[ 406.159415][ C3] ext4_buffered_write_iter+0x244/0x4d0
[ 406.159422][ C3] ext4_file_write_iter+0x423/0x14e0
[ 406.159429][ C3] ? ext4_buffered_write_iter+0x4d0/0x4d0
[ 406.159437][ C3] ? lockdep_hardirqs_on_prepare+0x400/0x400
[ 406.159444][ C3] ? __sanitizer_cov_trace_const_cmp4+0x1c/0x70
[ 406.159452][ C3] new_sync_write+0x426/0x650
[ 406.159458][ C3] ? new_sync_read+0x6e0/0x6e0
[ 406.159464][ C3] ? lock_release+0x720/0x720
[ 406.159470][ C3] vfs_write+0x796/0xa30
[ 406.159476][ C3] ksys_write+0x12d/0x250
[ 406.159482][ C3] ? __ia32_sys_read+0xb0/0xb0
[ 406.159489][ C3] ? syscall_enter_from_user_mode+0x27/0x70
[ 406.159496][ C3] do_syscall_64+0x2d/0x70
[ 406.159502][ C3] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 406.159509][ C3] RIP: 0033:0x7f98b160b19d
[ 406.159521][ C3] Code: d1 20 00 00 75 10 b8 01 00 00 00 0f 05 48
3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 be fa ff ff 48 89 04 24 b8 01
00 00 00 0f 05 <48> 8b 3c 241
[ 406.159539][ C3] RSP: 002b:00007f98afbac000 EFLAGS: 00000293
ORIG_RAX: 0000000000000001
[ 406.159555][ C3] RAX: ffffffffffffffda RBX: 0000000000000335
RCX: 00007f98b160b19d
[ 406.159565][ C3] RDX: 0000000000000335 RSI: 0000000001385a90
RDI: 0000000000000005
[ 406.159575][ C3] RBP: 0000000001385a90 R08: 0000000001385db5
R09: 00007f98b0f88547
[ 406.159585][ C3] R10: 0000000000000000 R11: 0000000000000293
R12: 0000000000000000
[ 406.159595][ C3] R13: 00007f98afbac480 R14: 0000000000000013
R15: 0000000001385870
[ 406.159613][ T1651] Kernel panic - not syncing: hung_task: blocked tasks
[ 406.211961][ T1651] CPU: 0 PID: 1651 Comm: khungtaskd Not tainted
5.12.0-rc5-next-20210330 #113
[ 406.213144][ T1651] Hardware name: QEMU Standard PC (Q35 + ICH9,
2009), BIOS rel-1.13.0-44-g88ab0c15525c-prebuilt.qemu.org 04/01/2014
[ 406.214758][ T1651] Call Trace:
[ 406.215259][ T1651] dump_stack+0x141/0x1d7
[ 406.215844][ T1651] panic+0x306/0x73d
[ 406.216373][ T1651] ? __warn_printk+0xf3/0xf3
[ 406.216994][ T1651] ? cpumask_next+0x3c/0x40
[ 406.217603][ T1651] ? __sanitizer_cov_trace_cmp4+0x1c/0x70
[ 406.218370][ T1651] ? printk_safe_flush+0xea/0x160
[ 406.219056][ T1651] ? watchdog.cold+0x22d/0x248
[ 406.219704][ T1651] watchdog.cold+0x23e/0x248
[ 406.220345][ T1651] ? trace_sched_process_hang+0x280/0x280
[ 406.221121][ T1651] kthread+0x3b1/0x4a0
[ 406.221679][ T1651] ? __kthread_bind_mask+0xc0/0xc0
[ 406.222375][ T1651] ret_from_fork+0x1f/0x30
[ 406.224241][ T1651] Kernel Offset: disabled
[ 406.224783][ T1651] Rebooting in 86400 seconds..

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.