[v6.1] INFO: task hung in __fdget_pos (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7b34dc04e4ff Linux 6.1.154
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16750092580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7eb38bd5021fec61
dashboard link: https://syzkaller.appspot.com/bug?extid=d253aa45c0832e0f13b3
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10abf27c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=145305cd980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1f1ed5df43e0/disk-7b34dc04.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/941b7c0f58be/vmlinux-7b34dc04.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6fb9bad299e4/bzImage-7b34dc04.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d253aa...@syzkaller.appspotmail.com

INFO: task syz.0.17:4460 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:29184 pid:4460 ppid:4384 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5244 [inline]
__schedule+0x10ec/0x40b0 kernel/sched/core.c:6561
schedule+0xb9/0x180 kernel/sched/core.c:6637
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6696
__mutex_lock_common kernel/locking/mutex.c:679 [inline]
__mutex_lock+0x555/0xaf0 kernel/locking/mutex.c:747
__fdget_pos+0x2ae/0x360 fs/file.c:1038
fdget_pos include/linux/file.h:74 [inline]
__do_sys_getdents64 fs/readdir.c:365 [inline]
__se_sys_getdents64+0xbe/0x260 fs/readdir.c:354
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f2328b8eec9
RSP: 002b:00007f23281fe038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f2328de6090 RCX: 00007f2328b8eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 00007f2328c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2328de6128 R14: 00007f2328de6090 R15: 00007ffc5a1db028
</TASK>

Showing all locks held in the system:
1 lock held by rcu_tasks_kthre/12:
#0: ffffffff8cb2b570 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x33/0xf00 kernel/rcu/tasks.h:517
1 lock held by rcu_tasks_trace/13:
#0: ffffffff8cb2bd90 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x33/0xf00 kernel/rcu/tasks.h:517
1 lock held by khungtaskd/28:
#0: ffffffff8cb2abe0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
#0: ffffffff8cb2abe0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
#0: ffffffff8cb2abe0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x51/0x290 kernel/locking/lockdep.c:6513
2 locks held by getty/4028:
#0: ffff8880300fd098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:244
#1: ffffc9000327e2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x41b/0x1380 drivers/tty/n_tty.c:2198
2 locks held by syz.0.17/4459:
#0: ffff88802f204868 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b458150 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.0.17/4460:
#0: ffff88802f204868 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by kworker/u4:6/4461:
2 locks held by syz.1.18/4483:
#0: ffff88807d48a0e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b560150 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.1.18/4484:
#0: ffff88807d48a0e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.2.19/4512:
#0: ffff888078368d68 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b560728 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.2.19/4513:
#0: ffff888078368d68 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.3.20/4535:
#0: ffff8880281da0e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b560d00 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.3.20/4536:
#0: ffff8880281da0e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.4.21/4564:
#0: ffff88807d38eae8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b458728 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.4.21/4565:
#0: ffff88807d38eae8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.5.22/4593:
#0: ffff88807c12aae8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b5612d8 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.5.22/4594:
#0: ffff88807c12aae8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.6.23/4627:
#0: ffff88807baf9268 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b5618b0 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.6.23/4628:
#0: ffff88807baf9268 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.7.24/4655:
#0: ffff88807c589768 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b561e88 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.7.24/4657:
#0: ffff88807c589768 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
2 locks held by syz.8.25/4684:
#0: ffff8880789514e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038
#1: ffff88805b562460 (&sb->s_type->i_mutex_key#21){.+.+}-{3:3}, at: iterate_dir+0x10d/0x560 fs/readdir.c:55
1 lock held by syz.8.25/4686:
#0: ffff8880789514e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2ae/0x360 fs/file.c:1038

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

NMI backtrace for cpu 0
CPU: 0 PID: 28 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
nmi_cpu_backtrace+0x3f4/0x470 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x1d4/0x450 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:220 [inline]
watchdog+0xeee/0xf30 kernel/hung_task.c:377
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4461 Comm: kworker/u4:6 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: events_unbound nsim_dev_trap_report_work
RIP: 0010:check_preemption_disabled+0x1/0x110 lib/smp_processor_id.c:13
Code: 20 74 bc 8c 4c 89 f6 e8 fd 1c 17 fa e9 6e ff ff ff 00 00 cc cc 00 00 cc cc 48 c7 c7 80 fc de 8a 48 c7 c6 c0 fc de 8a eb 00 55 <41> 57 41 56 53 48 83 ec 10 65 48 8b 04 25 28 00 00 00 48 89 44 24
RSP: 0018:ffffc900035577f8 EFLAGS: 00000046
RAX: 0000000080000001 RBX: ffffffff847a3d39 RCX: ffff88807b035940
RDX: 0000000000000000 RSI: ffffffff8a8c0520 RDI: ffffffff8adefce0
RBP: ffffc900035579f0 R08: dffffc0000000000 R09: ffffc90003557a80
R10: fffff520006aaf58 R11: 1ffff920006aaf50 R12: ffffc90003557900
R13: 0000000000000002 R14: 0000000000000200 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055ef72df2a38 CR3: 000000000c88e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
lockdep_hardirqs_off+0xa7/0x100 kernel/locking/lockdep.c:4400
trace_hardirqs_off+0xe/0x40 kernel/trace/trace_preemptirq.c:76
crng_make_state+0x159/0xa90 drivers/char/random.c:328
_get_random_bytes+0xd2/0x210 drivers/char/random.c:366
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:776 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline]
nsim_dev_trap_report_work+0x650/0xaf0 drivers/net/netdevsim/dev.c:851
process_one_work+0x898/0x1160 kernel/workqueue.c:2292
worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>


---
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