[syzbot] [net?] WARNING: locking bug in finish_task_switch (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ccd1cdca5cd4 Merge tag 'nfsd-6.19-1' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1417109a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1f2b6fe1fdf1a00b
dashboard link: https://syzkaller.appspot.com/bug?extid=fa2e2b8fd1b3f689d484
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7a2605cdbf37/disk-ccd1cdca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1a90296b9771/vmlinux-ccd1cdca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/01272b1902ce/bzImage-ccd1cdca.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fa2e2b...@syzkaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(1)
WARNING: kernel/locking/lockdep.c:238 at hlock_class kernel/locking/lockdep.c:238 [inline], CPU#0: ktimers/0/16
WARNING: kernel/locking/lockdep.c:238 at check_wait_context kernel/locking/lockdep.c:4879 [inline], CPU#0: ktimers/0/16
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x55a/0x2cf0 kernel/locking/lockdep.c:5187, CPU#0: ktimers/0/16
Modules linked in:
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 10/25/2025
RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline]
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4879 [inline]
RIP: 0010:__lock_acquire+0x561/0x2cf0 kernel/locking/lockdep.c:5187
Code: 83 3d a2 bd 21 17 00 75 27 90 e8 ba 99 dd 02 85 c0 74 1c 83 3d c3 bd 3e 0d 00 75 13 48 8d 3d d6 c1 41 0d 48 c7 c6 ca 31 ee 8c <67> 48 0f b9 3a 90 31 c9 0f b6 81 c4 00 00 00 84 c0 0f 84 77 ff ff
RSP: 0018:ffffc900001571b0 EFLAGS: 00010046
RAX: 0000000000000001 RBX: ffff88801b6de760 RCX: ffff88801b6ddac0
RDX: 0000000000000100 RSI: ffffffff8cee31ca RDI: ffffffff8ede4890
RBP: ffff88801b6de768 R08: 0000000000000000 R09: 0000000000000100
R10: dffffc0000000000 R11: fffffbfff1db688f R12: 0000000000000003
R13: ffff88801b6de768 R14: ffff88801b6ddac0 R15: 0000000000000006
FS: 0000000000000000(0000) GS:ffff888126cef000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2f617ff8 CR3: 0000000033f24000 CR4: 00000000003526f0
Call Trace:
<TASK>
lock_acquire+0x107/0x340 kernel/locking/lockdep.c:5868
finish_lock_switch kernel/sched/core.c:4993 [inline]
finish_task_switch+0x177/0x940 kernel/sched/core.c:5112
context_switch kernel/sched/core.c:5259 [inline]
__schedule+0x1467/0x5070 kernel/sched/core.c:6863
__schedule_loop kernel/sched/core.c:6945 [inline]
schedule_rtlock+0x30/0x70 kernel/sched/core.c:7024
rtlock_slowlock_locked+0x3819/0x4010 kernel/locking/rtmutex.c:1868
rtlock_slowlock kernel/locking/rtmutex.c:1895 [inline]
rtlock_lock kernel/locking/spinlock_rt.c:43 [inline]
__rt_spin_lock kernel/locking/spinlock_rt.c:49 [inline]
rt_spin_lock+0x158/0x3e0 kernel/locking/spinlock_rt.c:57
spin_lock include/linux/spinlock_rt.h:44 [inline]
fq_pie_timer+0x190/0x5b0 net/sched/sch_fq_pie.c:397
call_timer_fn+0x16e/0x590 kernel/time/timer.c:1748
expire_timers kernel/time/timer.c:1799 [inline]
__run_timers kernel/time/timer.c:2373 [inline]
__run_timer_base+0x648/0x970 kernel/time/timer.c:2385
run_timer_base kernel/time/timer.c:2394 [inline]
run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2404
handle_softirqs+0x1df/0x650 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
run_ktimerd+0x69/0x100 kernel/softirq.c:1138
smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
----------------
Code disassembly (best guess):
0: 83 3d a2 bd 21 17 00 cmpl $0x0,0x1721bda2(%rip) # 0x1721bda9
7: 75 27 jne 0x30
9: 90 nop
a: e8 ba 99 dd 02 call 0x2dd99c9
f: 85 c0 test %eax,%eax
11: 74 1c je 0x2f
13: 83 3d c3 bd 3e 0d 00 cmpl $0x0,0xd3ebdc3(%rip) # 0xd3ebddd
1a: 75 13 jne 0x2f
1c: 48 8d 3d d6 c1 41 0d lea 0xd41c1d6(%rip),%rdi # 0xd41c1f9
23: 48 c7 c6 ca 31 ee 8c mov $0xffffffff8cee31ca,%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 90 nop
30: 31 c9 xor %ecx,%ecx
32: 0f b6 81 c4 00 00 00 movzbl 0xc4(%rcx),%eax
39: 84 c0 test %al,%al
3b: 0f .byte 0xf
3c: 84 77 ff test %dh,-0x1(%rdi)
3f: ff .byte 0xff


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