[v6.6] INFO: rcu detected stall in kthread

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 924b4a879cbb Linux 6.6.142
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16140bd2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=90249d2d52c08134
dashboard link: https://syzkaller.appspot.com/bug?extid=f3c8bdf0b0d50acca57a
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11c1d8ae580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bd13425862f1/disk-924b4a87.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/eaa5de9e440b/vmlinux-924b4a87.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5a9aa3293c15/bzImage-924b4a87.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f3c8bd...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 0, t=10502 jiffies, g=26745, q=233 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10502 (4295006138-4294995636), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g26745 f0x2 RCU_GP_DOING_FQS(6) ->state=0x0 ->cpu=0
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt state:R running task stack:26568 pid:17 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x1553/0x45a0 kernel/sched/core.c:6700
preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
irqentry_exit+0x67/0x70 kernel/entry/common.c:438
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:rcu_gp_fqs_loop+0x156e/0x1590 kernel/rcu/tree.c:1717
Code: e0 45 48 8b 44 24 40 48 c7 04 30 00 00 00 00 c7 44 30 08 00 00 00 00 65 48 8b 04 25 28 00 00 00 48 3b 84 24 20 01 00 00 75 0f <48> 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 0e 0b 16 09 66 2e
RSP: 0018:ffffc90000167c80 EFLAGS: 00000246
RAX: 0b227e94a327bd00 RBX: 0000000000000000 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: dffffc0000000000 RDI: 00000000ffffffff
RBP: ffffc90000167df0 R08: ffffffff8e8b666f R09: 1ffffffff1d16ccd
R10: dffffc0000000000 R11: fffffbfff1d16cce R12: ffff88801ba41c00
R13: ffffc90000067740 R14: ffffc90000167d68 R15: 0000000000000002
rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
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>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 PID: 9677 Comm: syz.1.1788 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x29/0x50 kernel/locking/spinlock.c:202
Code: 00 f3 0f 1e fa 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 0a ac d6 f6 48 89 df e8 c2 80 d7 f6 e8 bd 98 fb f6 fb bf 01 00 00 00 <e8> a2 87 ca f6 65 8b 05 33 b0 71 75 85 c0 74 02 5b c3 e8 30 97 6e
RSP: 0018:ffffc9000445fc78 EFLAGS: 00000286
RAX: c90b5fd3cf582300 RBX: ffff888076428000 RCX: c90b5fd3cf582300
RDX: dffffc0000000000 RSI: ffffffff8acacbe0 RDI: 0000000000000001
RBP: ffff888076428498 R08: ffffffff8e8b666f R09: 1ffffffff1d16ccd
R10: dffffc0000000000 R11: fffffbfff1d16cce R12: 1ffff1100ec85093
R13: 0000000000000021 R14: dffffc0000000000 R15: 0000000000000000
FS: 00007f8b50b8d6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 000000005e5c3000 CR4: 00000000003506f0
Call Trace:
<TASK>
spin_unlock_irq include/linux/spinlock.h:401 [inline]
get_signal+0x11f5/0x13f0 kernel/signal.c:2905
arch_do_signal_or_restart+0xc2/0x800 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f8b4fd9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8b50b8d0e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f8b50015fa8 RCX: 00007f8b4fd9ce59
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f8b50015fa8
RBP: 00007f8b50015fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8b50016038 R14: 00007ffdcbc45aa0 R15: 00007ffdcbc45b88
</TASK>
sched: RT throttling activated


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