Re: [syzbot] [kernfs?] INFO: task hung in fdget_pos

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    09f6b0c8904b Merge tag 'linux_kselftest-fixes-6.12-rc3' of..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d43fd0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7cd9e7e4a8a0a15b
dashboard link: https://syzkaller.appspot.com/bug?extid=0ee1ef35cf7e70ce55d7
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=104a7b27980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11cee087980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-09f6b0c8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3844cfd6d6b9/vmlinux-09f6b0c8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8752e101c1ff/bzImage-09f6b0c8.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/f596198b5b58/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0ee1ef35cf7e70ce55d7@xxxxxxxxxxxxxxxxxxxxxxxxx

INFO: task syz-executor219:5184 blocked for more than 143 seconds.
      Not tainted 6.12.0-rc2-syzkaller-00291-g09f6b0c8904b #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor219 state:D stack:28952 pid:5184  tgid:5133  ppid:5129   flags:0x00000006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5322 [inline]
 __schedule+0x1895/0x4b30 kernel/sched/core.c:6682
 __schedule_loop kernel/sched/core.c:6759 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6774
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6831
 __mutex_lock_common kernel/locking/mutex.c:684 [inline]
 __mutex_lock+0x6a7/0xd70 kernel/locking/mutex.c:752
 fdget_pos+0x24e/0x320 fs/file.c:1160
 ksys_read+0x7e/0x2b0 fs/read_write.c:703
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f59323ec4b9
RSP: 002b:00007f5932382238 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f593247d618 RCX: 00007f59323ec4b9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007f593247d610 R08: 00007ffd45f51bd7 R09: 00007f59323826c0
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f59324400c0
R13: 000000000000006e R14: 00007ffd45f51af0 R15: 00007ffd45f51bd8
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/25:
 #0: ffffffff8e937de0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #0: ffffffff8e937de0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffffffff8e937de0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6720
1 lock held by kswapd0/75:
1 lock held by kswapd1/80:
 #0: ffff88801fc3ea98 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:593
2 locks held by getty/4903:
 #0: ffff88801ece10a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000039b2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6a6/0x1e00 drivers/tty/n_tty.c:2211
4 locks held by syz-executor219/5142:
1 lock held by syz-executor219/5184:
 #0: ffff8880366bf478 (&f->f_pos_lock){+.+.}-{3:3}, at: fdget_pos+0x24e/0x320 fs/file.c:1160

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 25 Comm: khungtaskd Not tainted 6.12.0-rc2-syzkaller-00291-g09f6b0c8904b #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x49c/0x4d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x198/0x320 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:223 [inline]
 watchdog+0xff4/0x1040 kernel/hung_task.c:379
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


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