[syzbot] [fuse?] INFO: task hung in fuse_chan_send

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c425609d6ac4 Add linux-next specific files for 20260612
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1206c3b6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d7a56b1e89b63439
dashboard link: https://syzkaller.appspot.com/bug?extid=a531d1b1fb0fa2a75a73
compiler: Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=163c04ae580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7fab9a8df61a/disk-c425609d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c2577196651b/vmlinux-c425609d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/053557a7471e/bzImage-c425609d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a531d1...@syzkaller.appspotmail.com

INFO: task syz.0.17:5995 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:27344 pid:5995 tgid:5994 ppid:5839 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5504 [inline]
__schedule+0x1709/0x5530 kernel/sched/core.c:7228
__schedule_loop kernel/sched/core.c:7307 [inline]
schedule+0x164/0x360 kernel/sched/core.c:7322
request_wait_answer fs/fuse/dev.c:743 [inline]
__fuse_request_send fs/fuse/dev.c:757 [inline]
fuse_chan_send+0x1068/0x1ad0 fs/fuse/dev.c:833
fuse_simple_request fs/fuse/fuse_i.h:1012 [inline]
fuse_do_getattr+0x370/0x690 fs/fuse/dir.c:1505
fuse_update_get_attr+0x600/0x1300 fs/fuse/dir.c:1562
vfs_getattr_nosec+0x2e1/0x430 fs/stat.c:213
vfs_statx_path+0x2b/0x230 fs/stat.c:299
vfs_statx+0x12e/0x200 fs/stat.c:356
vfs_fstatat+0x11b/0x170 fs/stat.c:373
__do_sys_newfstatat fs/stat.c:538 [inline]
__se_sys_newfstatat fs/stat.c:532 [inline]
__x64_sys_newfstatat+0x151/0x200 fs/stat.c:532
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0189d9ce59
RSP: 002b:00007f01893fe028 EFLAGS: 00000246 ORIG_RAX: 0000000000000106
RAX: ffffffffffffffda RBX: 00007f018a015fa0 RCX: 00007f0189d9ce59
RDX: 0000000000000000 RSI: 0000200000000500 RDI: ffffffffffffff9c
RBP: 00007f0189e32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000001000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f018a016038 R14: 00007f018a015fa0 R15: 00007ffef89eaea8
</TASK>

Showing all locks held in the system:
10 locks held by ktimers/0/16:
#0: ffffffff8de611a0 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
#1: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
#2: ffff8880b8626260 (&base->expiry_lock){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
#2: ffff8880b8626260 (&base->expiry_lock){+...}-{3:3}, at: timer_base_lock_expiry kernel/time/timer.c:1502 [inline]
#2: ffff8880b8626260 (&base->expiry_lock){+...}-{3:3}, at: __run_timer_base+0x11a/0x9b0 kernel/time/timer.c:2384
#3: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#3: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#3: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
#3: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
#4: ffffc90000157a80 ((&ndev->rs_timer)){+...}-{0:0}, at: expire_timers kernel/time/timer.c:1800 [inline]
#4: ffffc90000157a80 ((&ndev->rs_timer)){+...}-{0:0}, at: __run_timers kernel/time/timer.c:2374 [inline]
#4: ffffc90000157a80 ((&ndev->rs_timer)){+...}-{0:0}, at: __run_timer_base+0x683/0x9b0 kernel/time/timer.c:2386
#5: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
#6: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#6: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#6: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
#6: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
#7: ffffffff8de611a0 (local_bh){.+.+}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#7: ffffffff8de611a0 (local_bh){.+.+}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#7: ffffffff8de611a0 (local_bh){.+.+}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
#7: ffffffff8de611a0 (local_bh){.+.+}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
#8: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: debug_object_activate+0xa8/0x3a0 lib/debugobjects.c:873
#9: ffff888037258af8 (&p->pi_lock){-...}-{2:2}, at: class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:572 [inline]
#9: ffff888037258af8 (&p->pi_lock){-...}-{2:2}, at: try_to_wake_up+0x67/0x1430 kernel/sched/core.c:4292
1 lock held by khungtaskd/39:
#0: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#0: ffffffff8dfcb040 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6777
2 locks held by getty/5363:
#0: ffff8880365650a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc90003cc62e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x460/0x1360 drivers/tty/n_tty.c:2211

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 39 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:122
nmi_trigger_cpumask_backtrace+0x17a/0x380 lib/nmi_backtrace.c:65
trigger_all_cpu_backtrace include/linux/nmi.h:162 [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:353 [inline]
watchdog+0xfd7/0x1030 kernel/hung_task.c:561
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:__find_rr_leaf+0x121/0x760 net/ipv6/route.c:840
Code: c0 33 c1 8d 48 c1 e8 03 48 89 44 24 70 4c 89 7c 24 38 4d 85 ff 74 4e 49 8d 9e 90 00 00 00 48 89 d8 48 c1 e8 03 42 0f b6 04 28 <84> c0 75 21 8b 1b 89 df 44 8b 64 24 4c 44 89 e6 e8 9a 71 e5 f7 44
RSP: 0018:ffffc90000157160 EFLAGS: 00000a02
RAX: 0000000000000000 RBX: ffff888036f70490 RCX: ffff88801d688000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: ffffc900001572b8 R08: 0000000000000000 R09: 0000000000000100
R10: ffffc90000157240 R11: fffff5200002ae4a R12: 1ffff1100783a48c
R13: dffffc0000000000 R14: ffff888036f70400 R15: ffffc900001573b8
FS: 0000000000000000(0000) GS:ffff888125ece000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000559e696cf1f0 CR3: 000000002a2d2000 CR4: 00000000003526f0
Call Trace:
<TASK>
find_rr_leaf net/ipv6/route.c:892 [inline]
rt6_select net/ipv6/route.c:936 [inline]
fib6_table_lookup+0x3cb/0xb00 net/ipv6/route.c:2254
ip6_pol_route+0x228/0x13e0 net/ipv6/route.c:2290
pol_lookup_func include/net/ip6_fib.h:669 [inline]
fib6_rule_lookup+0x563/0x740 net/ipv6/fib6_rules.c:123
ip6_route_input_lookup net/ipv6/route.c:2359 [inline]
ip6_route_input+0x78d/0xb20 net/ipv6/route.c:2662
ip6_rcv_finish+0x141/0x280 net/ipv6/ip6_input.c:117
NF_HOOK+0x336/0x3c0 include/linux/netfilter.h:318
__netif_receive_skb_one_core net/core/dev.c:6205 [inline]
__netif_receive_skb net/core/dev.c:6318 [inline]
process_backlog+0x3bf/0xc50 net/core/dev.c:6669
__napi_poll+0xae/0x550 net/core/dev.c:7728
napi_poll net/core/dev.c:7791 [inline]
net_rx_action+0x621/0xd70 net/core/dev.c:7948
handle_softirqs+0x1d9/0x6c0 kernel/softirq.c:626
__do_softirq kernel/softirq.c:660 [inline]
run_ktimerd+0x69/0x100 kernel/softirq.c:1155
smpboot_thread_fn+0x57c/0xa80 kernel/smpboot.c:160
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


---
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