[syzbot] [kernfs?] [squashfs?] INFO: task hung in seq_read_iter

[syzbot <syzbot+6ecf4a3421e93925761b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    92fd6e84175b Add linux-next specific files for 20251125
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12495612580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bf77a4e0e3514deb
dashboard link: https://syzkaller.appspot.com/bug?extid=6ecf4a3421e93925761b
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=117ef8b4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bee2604d495b/disk-92fd6e84.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b12aade49e2c/vmlinux-92fd6e84.xz
kernel image: https://storage.googleapis.com/syzbot-assets/286fd34158cb/bzImage-92fd6e84.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/33772c2cfc52/mount_15.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6ecf4a3421e93925761b@syzkaller.appspotmail.com

INFO: task syz.1.22:6110 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.22        state:D stack:28568 pid:6110  tgid:6108  ppid:5947   task_flags:0x400040 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5257 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6864
 __schedule_loop kernel/sched/core.c:6946 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6961
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7018
 __mutex_lock_common kernel/locking/mutex.c:686 [inline]
 __mutex_lock+0x7e6/0x1350 kernel/locking/mutex.c:770
 seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
 seq_read+0x369/0x480 fs/seq_file.c:162
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x5aa/0x850 fs/read_write.c:1020
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x197/0x2a0 fs/read_write.c:1174
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f068378f749
RSP: 002b:00007f06846af038 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00007f06839e6090 RCX: 00007f068378f749
RDX: 0000000000000001 RSI: 00002000000005c0 RDI: 0000000000000004
RBP: 00007f0683813f91 R08: 00000000ffffffff R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f06839e6128 R14: 00007f06839e6090 R15: 00007fff64457eb8
 </TASK>
INFO: task syz.2.37:6190 blocked for more than 145 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.37        state:D stack:28568 pid:6190  tgid:6188  ppid:5950   task_flags:0x400040 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5257 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6864
 __schedule_loop kernel/sched/core.c:6946 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6961
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7018
 __mutex_lock_common kernel/locking/mutex.c:686 [inline]
 __mutex_lock+0x7e6/0x1350 kernel/locking/mutex.c:770
 seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
 seq_read+0x369/0x480 fs/seq_file.c:162
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x5aa/0x850 fs/read_write.c:1020
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x197/0x2a0 fs/read_write.c:1174
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe8e338f749
RSP: 002b:00007fe8e4250038 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00007fe8e35e6090 RCX: 00007fe8e338f749
RDX: 0000000000000001 RSI: 00002000000005c0 RDI: 0000000000000004
RBP: 00007fe8e3413f91 R08: 00000000ffffffff R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe8e35e6128 R14: 00007fe8e35e6090 R15: 00007ffcdac37898
 </TASK>

Showing all locks held in the system:
1 lock held by rcu_exp_gp_kthr/18:
1 lock held by khungtaskd/31:
 #0: ffffffff8df3d820 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8df3d820 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8df3d820 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
2 locks held by getty/5580:
 #0: ffff8880301e20a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000331e2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x449/0x1460 drivers/tty/n_tty.c:2211
2 locks held by syz.1.22/6109:
1 lock held by syz.1.22/6110:
 #0: ffff88806a07ad58 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.2.37/6189:
1 lock held by syz.2.37/6190:
 #0: ffff8880310702f0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.4.48/6272:
1 lock held by syz.4.48/6274:
 #0: ffff88807f09cd58 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.3.52/6298:
1 lock held by syz.3.52/6299:
 #0: ffff88807f24f790 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.0.54/6320:
1 lock held by syz.0.54/6322:
 #0: ffff888030fa7668 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.6.50/6338:
1 lock held by syz.6.50/6339:
 #0: ffff88802f4eab08 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.5.56/6346:
1 lock held by syz.5.56/6347:
 #0: ffff88802f4ea9e0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.7.57/6438:
1 lock held by syz.7.57/6440:
 #0: ffff88802f4ea668 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
1 lock held by syz.9.59/6493:
1 lock held by syz.9.59/6494:
 #0: ffff888077bdbc30 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.8.63/6503:
1 lock held by syz.8.63/6506:
 #0: ffff88802fcb41c8 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.2.61/6513:
1 lock held by syz.2.61/6517:
 #0: ffff88807f09c790 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.1.64/6537:
2 locks held by syz.4.62/6568:
1 lock held by syz.4.62/6569:
 #0: ffff8880286b59e0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.3.65/6687:
1 lock held by syz.3.65/6689:
 #0: ffff888030fa7790 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.6.67/6700:
1 lock held by syz.6.67/6701:
 #0: ffff88807743e0a0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.0.66/6699:
1 lock held by syz.0.66/6703:
 #0: ffff88807743e1c8 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.5.68/6707:
1 lock held by syz.5.68/6708:
 #0: ffff88802fcb40a0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
2 locks held by syz.7.69/6712:
1 lock held by syz.7.69/6713:
 #0: ffff88802fcb4668 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
9 locks held by syz-executor/6719:
 #0: ffff888033e4e420 (sb_writers#7){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2681 [inline]
 #0: ffff888033e4e420 (sb_writers#7){.+.+}-{0:0}, at: vfs_write+0x211/0xb30 fs/read_write.c:682
 #1: ffff8880404c3488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1de/0x540 fs/kernfs/file.c:343
 #2: ffff888141fcf3c8 (kn->active#58){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:80 [inline]
 #2: ffff888141fcf3c8 (kn->active#58){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x231/0x540 fs/kernfs/file.c:344
 #3: ffffffff8eb71308 (nsim_bus_dev_list_lock){+.+.}-{4:4}, at: del_device_store+0xd1/0x360 drivers/net/netdevsim/bus.c:234
 #4: ffff88805bb400e8 (&dev->mutex){....}-{4:4}, at: device_lock include/linux/device.h:895 [inline]
 #4: ffff88805bb400e8 (&dev->mutex){....}-{4:4}, at: __device_driver_lock drivers/base/dd.c:1096 [inline]
 #4: ffff88805bb400e8 (&dev->mutex){....}-{4:4}, at: device_release_driver_internal+0xb6/0x800 drivers/base/dd.c:1294
 #5: ffff8880202d3250 (&devlink->lock_key#11){+.+.}-{4:4}, at: nsim_drv_remove+0x50/0x160 drivers/net/netdevsim/dev.c:1777
 #6: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: nsim_destroy+0xed/0x680 drivers/net/netdevsim/netdev.c:1175
 #7: ffff8880329ecd48 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2773 [inline]
 #7: ffff8880329ecd48 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: unregister_netdevice_many_notify+0x58b/0x2340 net/core/dev.c:12352
 #8: ffffffff8df432f8 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock kernel/rcu/tree_exp.h:311 [inline]
 #8: ffffffff8df432f8 (rcu_state.exp_mutex){+.+.}-{4:4}, at: synchronize_rcu_expedited+0x2f6/0x730 kernel/rcu/tree_exp.h:956
2 locks held by syz-executor/6731:
 #0: ffffffff8f7e22d8 (&ops->srcu#2){.+.+}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8f7e22d8 (&ops->srcu#2){.+.+}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8f7e22d8 (&ops->srcu#2){.+.+}-{0:0}, at: rtnl_link_ops_get+0x23/0x250 net/core/rtnetlink.c:570
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x8ec/0x1c90 net/core/rtnetlink.c:4071
2 locks held by syz-executor/6734:
 #0: ffffffff8f7e1730 (&ops->srcu#2){.+.+}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8f7e1730 (&ops->srcu#2){.+.+}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8f7e1730 (&ops->srcu#2){.+.+}-{0:0}, at: rtnl_link_ops_get+0x23/0x250 net/core/rtnetlink.c:570
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x8ec/0x1c90 net/core/rtnetlink.c:4071
4 locks held by kworker/u8:45/6739:
 #0: ffff8880b863a918 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:639
 #1: ffff8880b8624588 (psi_seq){-.-.}-{0:0}, at: psi_task_switch+0x53/0x880 kernel/sched/psi.c:933
 #2: ffff8880b86260d8 (&base->lock){-.-.}-{2:2}, at: __mod_timer+0x8ee/0xf30 kernel/time/timer.c:1117
 #3: ffffffff99ac5768 (&obj_hash[i].lock){-.-.}-{2:2}, at: debug_object_activate+0x87/0x540 lib/debugobjects.c:818
2 locks held by syz-executor/6743:
 #0: ffffffff8f2ce4f0 (pernet_ops_rwsem){++++}-{4:4}, at: copy_net_ns+0x3cc/0x570 net/core/net_namespace.c:577
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock_killable include/linux/rtnetlink.h:145 [inline]
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: register_netdev+0x18/0x60 net/core/dev.c:11497
2 locks held by syz-executor/6749:
 #0: ffffffff8f2ce4f0 (pernet_ops_rwsem){++++}-{4:4}, at: copy_net_ns+0x3cc/0x570 net/core/net_namespace.c:577
 #1: ffffffff8f2dba08 (rtnl_mutex){+.+.}-{4:4}, at: ip_tunnel_init_net+0x2ab/0x800 net/ipv4/ip_tunnel.c:1146

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xf95/0xfe0 kernel/hung_task.c:515
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6346 Comm: syz.5.56 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:get_current arch/x86/include/asm/current.h:25 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x8/0x90 kernel/kcov.c:314
Code: 48 89 44 11 20 c3 cc cc cc cc cc 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 8b 04 24 <65> 48 8b 14 25 08 50 79 92 65 8b 0d 58 ab b7 10 81 e1 00 01 ff 00
RSP: 0018:ffffc90004c2f538 EFLAGS: 00000206
RAX: ffffffff8b53f66b RBX: 0000000000000010 RCX: ffff88807a2d3d00
RDX: 0000000000000000 RSI: 0000000000000010 RDI: 000000000000000a
RBP: ffffc90004c2f660 R08: ffffc90004c2f5d7 R09: 0000000000000000
R10: ffffc90004c2f5c0 R11: fffff52000985ebb R12: 000000003b9a64b9
R13: 000000003b9a64b9 R14: ffffc9001a2bb8aa R15: 00ffffffffffff10
FS:  00007fa6aa9856c0(0000) GS:ffff888125e8b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f48c77556e8 CR3: 0000000025c92000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 number+0x2db/0xf60 lib/vsprintf.c:508
 vsnprintf+0x8e2/0xee0 lib/vsprintf.c:2910
 seq_vprintf fs/seq_file.c:391 [inline]
 seq_printf+0x178/0x270 fs/seq_file.c:406
 __io_uring_show_fdinfo io_uring/fdinfo.c:158 [inline]
 io_uring_show_fdinfo+0x9e4/0x18a0 io_uring/fdinfo.c:261
 seq_show+0x5ac/0x710 fs/proc/fd.c:68
 traverse+0x1ee/0x580 fs/seq_file.c:111
 seq_read_iter+0xd08/0xe20 fs/seq_file.c:195
 seq_read+0x369/0x480 fs/seq_file.c:162
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x5aa/0x850 fs/read_write.c:1020
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x197/0x2a0 fs/read_write.c:1174
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa6a9b8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa6aa985038 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00007fa6a9de5fa0 RCX: 00007fa6a9b8f749
RDX: 0000000000000001 RSI: 00002000000005c0 RDI: 0000000000000004
RBP: 00007fa6a9c13f91 R08: 00000000ffffffff R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa6a9de6038 R14: 00007fa6a9de5fa0 R15: 00007ffddfa99f78
 </TASK>


---
This report 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 syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup