[v6.6] INFO: task hung in do_exit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 258cf62a6dfd Linux 6.6.137
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15884a73980000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=f738748dd4e386d24e60
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13884a73980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1400f76c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8abd93876bdd/disk-258cf62a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/721d0cc7467a/vmlinux-258cf62a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7f2dfd911e3d/bzImage-258cf62a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f73874...@syzkaller.appspotmail.com

INFO: task syz.0.17:5947 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.17 state:D stack:25320 pid:5947 ppid:5908 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x1553/0x45a0 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
coredump_task_exit kernel/exit.c:436 [inline]
do_exit+0x4db/0x2460 kernel/exit.c:825
do_group_exit+0x21b/0x2d0 kernel/exit.c:1024
get_signal+0x12fc/0x13f0 kernel/signal.c:2902
arch_do_signal_or_restart+0xc2/0x800 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xa0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fdb1ad9cdd9
RSP: 002b:00007ffe70e0c248 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffdfc RBX: 000000000002a633 RCX: 00007fdb1ad9cdd9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fdb1b01609c
RBP: 0000000000000032 R08: 0000000000745d1e R09: 0000000000000000
R10: 00007ffe70e0c350 R11: 0000000000000246 R12: 00007ffe70e0c370
R13: 00007fdb1b01609c R14: 000000000002a665 R15: 00007ffe70e0c350
</TASK>
INFO: task syz.0.17:5949 blocked for more than 144 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.17 state:D stack:27920 pid:5949 ppid:5908 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x1553/0x45a0 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
schedule_timeout+0xc1/0x2d0 kernel/time/timer.c:2144
do_wait_for_common kernel/sched/completion.c:95 [inline]
__wait_for_common+0x3e4/0x6f0 kernel/sched/completion.c:116
wait_for_common kernel/sched/completion.c:127 [inline]
wait_for_completion_state+0x1c/0x40 kernel/sched/completion.c:264
coredump_wait fs/coredump.c:443 [inline]
do_coredump+0x8d9/0x24d0 fs/coredump.c:640
get_signal+0x1133/0x13f0 kernel/signal.c:2888
arch_do_signal_or_restart+0xc2/0x800 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xa0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fdb1ad9cdd9
RSP: 002b:00007fdb1bc420e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 00000000000000ca RBX: 00007fdb1b016098 RCX: 00007fdb1ad9cdd9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007fdb1b01609c
RBP: 00007fdb1b016090 R08: 0000000000745d1e R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdb1b016128 R14: 00007ffe70e0c000 R15: 00007ffe70e0c0e8
</TASK>

Showing all locks held in the system:
3 locks held by kworker/0:1/9:
1 lock held by khungtaskd/29:
#0: ffffffff8d1320e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
#0: ffffffff8d1320e0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
#0: ffffffff8d1320e0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
2 locks held by kworker/u4:5/77:
2 locks held by getty/5531:
#0: ffff88803187a0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000326e2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x433/0x1390 drivers/tty/n_tty.c:2217
1 lock held by syz.1.18/5973:
1 lock held by syz.2.19/5990:
1 lock held by syz.3.20/6009:
2 locks held by syz.4.21/6038:
1 lock held by syz.6.23/6094:
1 lock held by syz.7.24/6125:

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

NMI backtrace for cpu 0
CPU: 0 PID: 29 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a6/0x3e0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x17a/0x2f0 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
watchdog+0xf3d/0xf80 kernel/hung_task.c:379
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 6038 Comm: syz.4.21 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:check_preemption_disabled+0x42/0x110 lib/smp_processor_id.c:55
Code: 65 8b 05 bd 35 7d 75 65 8b 0d b2 35 7d 75 f7 c1 ff ff ff 7f 74 1f 65 48 8b 0c 25 28 00 00 00 48 3b 4c 24 08 0f 85 c4 00 00 00 <48> 83 c4 10 5b 41 5e 41 5f 5d c3 48 c7 04 24 00 00 00 00 9c 8f 04
RSP: 0018:ffffc900036279a8 EFLAGS: 00000046
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 892c461b87185d00
RDX: 0000000000000000 RSI: ffffffff8acad6c0 RDI: ffffffff8b1c8fa0
RBP: ffffc90003627ae8 R08: ffffffff8e8b19af R09: 1ffffffff1d16335
R10: dffffc0000000000 R11: fffffbfff1d16336 R12: 1ffff920006c4f48
R13: ffff88805e20e0a8 R14: 0000000000000246 R15: dffffc0000000000
FS: 00007f94bfa336c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555d047e64f0 CR3: 000000002fb54000 CR4: 00000000003506e0
Call Trace:
<TASK>
lockdep_recursion_inc kernel/locking/lockdep.c:462 [inline]
lock_acquire+0x164/0x420 kernel/locking/lockdep.c:5753
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xcc0 kernel/locking/mutex.c:747
io_cqring_do_overflow_flush+0x19/0x30 io_uring/io_uring.c:722
io_cqring_wait io_uring/io_uring.c:2646 [inline]
__do_sys_io_uring_enter io_uring/io_uring.c:3824 [inline]
__se_sys_io_uring_enter+0x1b65/0x2540 io_uring/io_uring.c:3714
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f94beb9cdd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f94bfa33028 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
RAX: ffffffffffffffda RBX: 00007f94bee15fa0 RCX: 00007f94beb9cdd9
RDX: 000000000000235c RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f94bec32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f94bee16038 R14: 00007f94bee15fa0 R15: 00007fff982780b8
</TASK>


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