[v6.6] INFO: task hung in d_alloc_parallel

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d1cfde2d5d15 Linux 6.6.143
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16d3ccfe580000
kernel config: https://syzkaller.appspot.com/x/.config?x=441765643cbfb8d
dashboard link: https://syzkaller.appspot.com/bug?extid=f6b7b094ac715f53c2d5
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=1544501c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4e37bcd98892/disk-d1cfde2d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/64b2ed856057/vmlinux-d1cfde2d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0a6949479d66/bzImage-d1cfde2d.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/09308a478c65/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f6b7b0...@syzkaller.appspotmail.com

INFO: task syz.0.17:5948 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:24912 pid:5948 ppid:5904 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x15ae/0x4660 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
d_wait_lookup fs/dcache.c:2633 [inline]
d_alloc_parallel+0xbd9/0x1590 fs/dcache.c:2715
lookup_open fs/namei.c:3421 [inline]
open_last_lookups fs/namei.c:3564 [inline]
path_openat+0x955/0x3270 fs/namei.c:3794
do_filp_open+0x1f2/0x430 fs/namei.c:3824
do_sys_openat2+0x134/0x1d0 fs/open.c:1421
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0x139/0x160 fs/open.c:1447
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f8006b9ce59
RSP: 002b:00007f8007af3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f8006e15fa0 RCX: 00007f8006b9ce59
RDX: 0000000000000000 RSI: 0000200000000040 RDI: ffffffffffffff9c
RBP: 00007f8006c32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8006e16038 R14: 00007f8006e15fa0 R15: 00007ffec88f4f68
</TASK>

Showing all locks held in the system:
2 locks held by kworker/1:0/23:
1 lock held by khungtaskd/28:
#0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
#0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
#0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
3 locks held by kworker/u4:4/67:
#0: ffff88802caa5d38 ((wq_completion)ipv6_addrconf){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#0: ffff88802caa5d38 ((wq_completion)ipv6_addrconf){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
#1: ffffc900015e7d00 ((work_completion)(&(&ifa->dad_work)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#1: ffffc900015e7d00 ((work_completion)(&(&ifa->dad_work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
#2: ffffffff8e3bfe48 (rtnl_mutex){+.+.}-{3:3}, at: addrconf_dad_work+0xce/0x1550 net/ipv6/addrconf.c:4181
1 lock held by kswapd0/87:
3 locks held by kworker/u4:6/2971:
#0: ffff888017c71538 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#0: ffff888017c71538 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
#1: ffffc9000b8a7d00 ((linkwatch_work).work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#1: ffffc9000b8a7d00 ((linkwatch_work).work){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
#2: ffffffff8e3bfe48 (rtnl_mutex){+.+.}-{3:3}, at: linkwatch_event+0xe/0x60 net/core/link_watch.c:286
3 locks held by kworker/u4:10/4605:
2 locks held by getty/5531:
#0: ffff888031e0a0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000327b2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x428/0x1370 drivers/tty/n_tty.c:2217
1 lock held by syz.0.17/5948:
#0: ffff88805e940198 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: inode_lock_shared include/linux/fs.h:814 [inline]
#0: ffff88805e940198 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: open_last_lookups fs/namei.c:3563 [inline]
#0: ffff88805e940198 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: path_openat+0x7e5/0x3270 fs/namei.c:3794
1 lock held by syz.0.17/5949:
1 lock held by syz.1.18/5966:
2 locks held by syz.2.19/5988:
1 lock held by syz.2.19/5989:
#0: ffff88805e9406e0 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: inode_lock_shared include/linux/fs.h:814 [inline]
#0: ffff88805e9406e0 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: lookup_slow+0x46/0x70 fs/namei.c:1718
1 lock held by syz.3.20/6007:
1 lock held by syz.4.21/6031:
1 lock held by syz.5.22/6061:
3 locks held by syz.6.23/6086:
1 lock held by syz.6.23/6087:
#0: ffff8880490a06e0 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: inode_lock_shared include/linux/fs.h:814 [inline]
#0: ffff8880490a06e0 (&type->i_mutex_dir_key#8){.+.+}-{3:3}, at: lookup_slow+0x46/0x70 fs/namei.c:1718
6 locks held by syz-executor/6090:
2 locks held by dhcpcd/6110:
#0: ffff88807a2b0130 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1780 [inline]
#0: ffff88807a2b0130 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: packet_do_bind+0x33/0xd40 net/packet/af_packet.c:3264
#1: ffffffff8d137778 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:292 [inline]
#1: ffffffff8d137778 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x306/0x880 kernel/rcu/tree_exp.h:1004

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

NMI backtrace for cpu 1
CPU: 1 PID: 28 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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+0xf59/0xfa0 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 9 Comm: kworker/0:1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: mld mld_ifc_work
RIP: 0010:deliver_ptype_list_skb net/core/dev.c:2289 [inline]
RIP: 0010:__netif_receive_skb_core+0x2bdd/0x3ab0 net/core/dev.c:5597
Code: 48 c1 e8 03 48 89 44 24 60 48 89 4c 24 30 48 c1 e9 03 48 89 4c 24 58 44 89 e3 4d 8d 77 c0 4c 89 f0 48 c1 e8 03 42 0f b6 04 28 <84> c0 0f 85 7c 02 00 00 45 0f b7 2e 44 89 ef 4c 8b 64 24 68 44 89
RSP: 0018:ffffc900000079a0 EFLAGS: 00000a02
RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffff88801a270000
RDX: 0000000000000100 RSI: 000000000000dd86 RDI: 0000000000000d00
RBP: ffffc90000007b70 R08: ffff88801a270000 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000100 R12: 0000000000000001
R13: dffffc0000000000 R14: ffffffff8e8ca570 R15: ffffffff8e8ca5b0
FS: 0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6bd874c7d8 CR3: 000000000cf32000 CR4: 00000000003506f0
Call Trace:
<IRQ>
__netif_receive_skb_one_core net/core/dev.c:5644 [inline]
__netif_receive_skb+0x74/0x290 net/core/dev.c:5760
process_backlog+0x380/0x710 net/core/dev.c:6088
__napi_poll+0xbb/0x460 net/core/dev.c:6650
napi_poll net/core/dev.c:6717 [inline]
net_rx_action+0x65f/0xcc0 net/core/dev.c:6853
handle_softirqs+0x27d/0x820 kernel/softirq.c:578
do_softirq+0xfa/0x1a0 kernel/softirq.c:479
</IRQ>
<TASK>
__local_bh_enable_ip+0x184/0x1c0 kernel/softirq.c:406
local_bh_enable include/linux/bottom_half.h:33 [inline]
rcu_read_unlock_bh include/linux/rcupdate.h:856 [inline]
__dev_queue_xmit+0x1bc2/0x3630 net/core/dev.c:4490
dev_queue_xmit include/linux/netdevice.h:3113 [inline]
neigh_hh_output include/net/neighbour.h:527 [inline]
neigh_output include/net/neighbour.h:541 [inline]
ip6_finish_output2+0xdf7/0x1620 net/ipv6/ip6_output.c:141
dst_output include/net/dst.h:467 [inline]
NF_HOOK+0x167/0x4a0 include/linux/netfilter.h:304
mld_sendpack+0x802/0xd60 net/ipv6/mcast.c:1823
mld_send_cr net/ipv6/mcast.c:2124 [inline]
mld_ifc_work+0x839/0xde0 net/ipv6/mcast.c:2654
process_one_work kernel/workqueue.c:2653 [inline]
process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2730
worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2811
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>


---
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