Re: [syzbot] [kernel?] INFO: task hung in futex_hash_allocate

[syzbot <syzbot+d6156c54e546fe8502c0@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in futex_hash_allocate

INFO: task syz.0.81:6865 blocked for more than 143 seconds.
      Not tainted 6.16.0-rc1-syzkaller-gf09079bd04a9-dirty #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.81        state:D stack:29288 pid:6865  tgid:6864  ppid:6537   task_flags:0x400040 flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5396 [inline]
 __schedule+0x116a/0x5de0 kernel/sched/core.c:6785
 __schedule_loop kernel/sched/core.c:6863 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6878
 futex_hash_allocate+0xd16/0xf10 kernel/futex/core.c:1619
 futex_hash_prctl+0x1f4/0x650 kernel/futex/core.c:1759
 __do_sys_prctl+0x171f/0x24c0 kernel/sys.c:2825
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f06a038e929
RSP: 002b:00007f06a12b6038 EFLAGS: 00000246 ORIG_RAX: 000000000000009d
RAX: ffffffffffffffda RBX: 00007f06a05b5fa0 RCX: 00007f06a038e929
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 000000000000004e
RBP: 00007f06a0410b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f06a05b5fa0 R15: 00007ffc811c5c98
 </TASK>

Showing all locks held in the system:
3 locks held by kworker/u8:1/13:
1 lock held by rcu_preempt/16:
 #0: ffff8880b853bdd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x29/0x130 kernel/sched/core.c:606
1 lock held by khungtaskd/31:
 #0: ffffffff8e3c46c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8e3c46c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #0: ffffffff8e3c46c0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x36/0x1c0 kernel/locking/lockdep.c:6770
2 locks held by kworker/u8:8/3529:
1 lock held by klogd/5195:
2 locks held by getty/5596:
 #0: ffff8880361ca0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000332b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x41b/0x14f0 drivers/tty/n_tty.c:2222

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted 6.16.0-rc1-syzkaller-gf09079bd04a9-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x27b/0x390 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x29c/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:307 [inline]
 watchdog+0xf70/0x12c0 kernel/hung_task.c:470
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 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: 36 Comm: kworker/u8:2 Not tainted 6.16.0-rc1-syzkaller-gf09079bd04a9-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: bat_events batadv_nc_worker
RIP: 0010:__lock_release kernel/locking/lockdep.c:5567 [inline]
RIP: 0010:lock_release+0x10b/0x2f0 kernel/locking/lockdep.c:5892
Code: 8d ff ff 48 85 c0 0f 84 47 01 00 00 8b 50 24 85 d2 0f 85 ae 01 00 00 66 83 78 22 1f 76 0c 66 83 68 22 20 66 83 78 22 1f 77 3c <8b> 54 24 0c 41 89 96 e8 0a 00 00 48 8b 00 49 89 86 e0 0a 00 00 41
RSP: 0018:ffffc90000ac7ae0 EFLAGS: 00000093
RAX: ffff888143ad2940 RBX: ffffffff8e3c46c0 RCX: ffffc90000ac7aec
RDX: 0000000000000000 RSI: ffffffff8e3c46c0 RDI: ffff888143ad2940
RBP: 00000000000000df R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: ffffffff8b492035
R13: 0000000000000206 R14: ffff888143ad1e00 R15: 0000000000000003
FS:  0000000000000000(0000) GS:ffff888124a62000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4c3ce51f98 CR3: 000000007572e000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 rcu_lock_release include/linux/rcupdate.h:341 [inline]
 rcu_read_unlock include/linux/rcupdate.h:871 [inline]
 batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:412 [inline]
 batadv_nc_worker+0x89a/0x1030 net/batman-adv/network-coding.c:719
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         f09079bd Merge tag 'powerpc-6.16-2' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15cb4d70580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c4c8362784bb7796
dashboard link: https://syzkaller.appspot.com/bug?extid=d6156c54e546fe8502c0
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12534d70580000