[Kernel Bug] INFO: rcu detected stall in sys_tgkill

[Longxing Li]

Dear Linux kernel developers and maintainers,

We would like to report a new kernel bug found by our tool. INFO: rcu
detected stall in sys_tgkill. Details are as follows.

Kernel commit: v7.0.6
Kernel config: see attachment
report: see attachment

We are currently analyzing the root cause and working on a
reproducible PoC. We will provide further updates in this thread as
soon as we have more information.

Best regards,
Longxing Li

==================================================================
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-0): P9690/1:b..l
rcu: (detected by 0, t=10502 jiffies, g=207237, q=1301 ncpus=1)
task:syz-fuzzer state:R running task stack:26712 pid:9690
tgid:9689 ppid:9683 task_flags:0x400040 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5298 [inline]
__schedule+0x1006/0x5f00 kernel/sched/core.c:6911
preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7238
irqentry_exit+0x1e4/0x740 kernel/entry/common.c:239
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x80 kernel/kcov.c:210
Code: 5d 41 5c 41 5d e9 50 25 bf 09 48 c7 c0 f4 ff ff ff eb 92 0f 1f
80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f
1e fa 48 8b 34 24 65 48 8b 15 d8 a2 2a 12 65 8b 05 e9 a2 2a
RSP: 0018:ffffc9000ac1fd18 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81bc9237
RDX: ffff88802a0c8000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: ffff888029a38000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000007 R12: 0000000000000017
R13: 0000000000000000 R14: ffffc9000ac1fe68 R15: 00000000000025d9
audit_signal_info+0xb5/0x190 kernel/audit.c:2759
check_kill_permission+0xb3/0x540 kernel/signal.c:811
do_send_specific+0x115/0x360 kernel/signal.c:4125
do_tkill kernel/signal.c:4152 [inline]
__do_sys_tgkill kernel/signal.c:4171 [inline]
__se_sys_tgkill kernel/signal.c:4165 [inline]
__x64_sys_tgkill+0x122/0x1a0 kernel/signal.c:4165
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x11b/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x479416
RSP: 002b:000000c000041e88 EFLAGS: 00000206 ORIG_RAX: 00000000000000ea
RAX: ffffffffffffffda RBX: 0000000000000017 RCX: 0000000000479416
RDX: 0000000000000017 RSI: 00000000000025e9 RDI: 00000000000025d9
RBP: 000000c000041ea8 R08: 0000000000006eb9 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 000000c000041928
R13: 000000c001173008 R14: 000000c000006540 R15: 01ffffffffffffff
</TASK>

https://drive.google.com/file/d/1Bx2unEf-QntjVi8g6Zw7QNO6OP4cjGO_/view?usp=drive_link

https://drive.google.com/file/d/13FO4UjAdiNA6tDG3cEii2sDY-pkR8AD-/view?usp=drive_link