syzbot
INFO: task hung in d_alloc_parallel (4)
Status:
upstream: reported C repro on 2026/09/16 15:42
Subsystems:
fs
Labels:
prio:high
[Documentation on labels]
Reported-by: syzbot+e8ebfecec06a009dd2d3@syzkaller.appspotmail.com
First crash: 2d05h, last: 1d19h
Sample crash report:
INFO: task syz-executor239:5636 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor239 state:D stack:28744 pid:5636 tgid:5633 ppid:5632 task_flags:0x400040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5526 [inline]
__schedule+0x16d9/0x5700 kernel/sched/core.c:7277
__schedule_loop kernel/sched/core.c:7354 [inline]
schedule+0x164/0x2b0 kernel/sched/core.c:7369
d_wait_lookup fs/dcache.c:2754 [inline]
d_alloc_parallel+0xd13/0x16c0 fs/dcache.c:2839
__lookup_slow+0x82/0x2f0 fs/namei.c:1904
lookup_slow+0x53/0x70 fs/namei.c:1936
walk_component fs/namei.c:2282 [inline]
link_path_walk+0xd2a/0x1910 fs/namei.c:2656
path_parentat fs/namei.c:2860 [inline]
__filename_parentat+0x287/0x6f0 fs/namei.c:2884
filename_parentat fs/namei.c:2902 [inline]
filename_create+0xd9/0x370 fs/namei.c:5073
filename_mkdirat+0xd2/0x520 fs/namei.c:5436
__do_sys_mkdirat fs/namei.c:5464 [inline]
__se_sys_mkdirat+0x35/0x150 fs/namei.c:5461
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3765e43349
RSP: 002b:00007f3765def1d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007f3765eeae38 RCX: 00007f3765e43349
RDX: 00000000000001c0 RSI: 0000200000000640 RDI: 00000000ffffff9c
RBP: 00007f3765eeae30 R08: 00007f3765def6c0 R09: 35203a6b63617473
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000640
R13: 0030656c69662f2e R14: 0000200000000280 R15: 0000200000000540
</TASK>
Showing all locks held in the system:
locks held by khungtaskd/37: 1, last CPU#0:
#0: ffffffff8e1c3c80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
#0: ffffffff8e1c3c80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
#0: ffffffff8e1c3c80 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6871
locks held by kworker/u8:7/1023: 2, on CPU#0:
#0: ffff88813ff64138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
#0: ffff88813ff64138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
#0: ffff88813ff64138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3361 [inline]
#0: ffff88813ff64138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3479
#1: ffffc90005277c40 ((work_completion)(&(&kfence_timer)->work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
#1: ffffc90005277c40 ((work_completion)(&(&kfence_timer)->work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
#1: ffffc90005277c40 ((work_completion)(&(&kfence_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3361 [inline]
#1: ffffc90005277c40 ((work_completion)(&(&kfence_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3479
locks held by getty/5350: 2, on CPU#1:
#0: ffff888036d190a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc900044d62e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x460/0x1360 drivers/tty/n_tty.c:2211
locks held by syz-executor239/5635: 1, last CPU#1:
#0: ffff888045d8bda0 (&type->i_mutex_dir_key#6){.+.+}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
#0: ffff888045d8bda0 (&type->i_mutex_dir_key#6){.+.+}-{4:4}, at: lookup_open+0x237/0x1a60 fs/namei.c:4460
locks held by syz-executor239/5636: 1, on CPU#0:
#0: ffff888045d8bda0 (&type->i_mutex_dir_key#6){.+.+}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
#0: ffff888045d8bda0 (&type->i_mutex_dir_key#6){.+.+}-{4:4}, at: lookup_slow+0x46/0x70 fs/namei.c:1935
=============================================
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/08/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:123
nmi_trigger_cpumask_backtrace+0x17d/0x390 lib/nmi_backtrace.c:66
trigger_all_cpu_backtrace include/linux/nmi.h:164 [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+0x38b/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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 5635 Comm: syz-executor239 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/08/2026
RIP: 0010:__might_sleep+0x31/0xf0 kernel/sched/core.c:9174
Code: 41 56 41 55 41 54 53 50 49 bf 00 00 00 00 00 fc ff df 65 48 8b 1d 87 17 0f 11 4c 8d 73 18 4c 89 f0 48 c1 e8 03 42 0f b6 04 38 <84> c0 0f 85 81 00 00 00 41 8b 2e 85 ed 74 2f 48 81 c3 90 18 00 00
RSP: 0018:ffffc90004c5f678 EFLAGS: 00000a02
RAX: 0000000000000000 RBX: ffff88801df83e80 RCX: ffff88801df83e80
RDX: 0000000000000000 RSI: 0000000000000142 RDI: ffffffff8d908f18
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff94000154819 R12: 0000000000000400
R13: 0000000000000400 R14: ffff88801df83e98 R15: dffffc0000000000
FS: 00007f3765e106c0(0000) GS:ffff888125ccb000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd25a71f52 CR3: 000000002ec1a000 CR4: 00000000003526f0
Call Trace:
<TASK>
might_alloc include/linux/sched/mm.h:322 [inline]
bdev_getblk+0xce/0x6e0 fs/buffer.c:1342
__bread_gfp+0x89/0x380 fs/buffer.c:1400
sb_bread include/linux/buffer_head.h:344 [inline]
romfs_blk_strcmp fs/romfs/storage.c:175 [inline]
romfs_dev_strcmp+0x3f8/0x790 fs/romfs/storage.c:284
romfs_lookup+0x232/0x3f0 fs/romfs/super.c:234
lookup_open+0x9eb/0x1a60 fs/namei.c:4528
open_last_lookups fs/namei.c:4767 [inline]
path_openat+0x67c/0x1d60 fs/namei.c:4997
do_file_open+0x23e/0x4a0 fs/namei.c:5029
do_sys_openat2+0x115/0x200 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3765e43349
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 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 d0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3765e101d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f3765eeae28 RCX: 00007f3765e43349
RDX: 0000000000000000 RSI: 0000200000000540 RDI: 00000000ffffff9c
RBP: 00007f3765eeae20 R08: 35203a6b63617473 R09: 35203a6b63617473
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000640
R13: 0030656c69662f2e R14: 0000200000000280 R15: 0000200000000540
</TASK>
Struck through repros no longer work on HEAD.