[v5.15] WARNING in rcu_check_gp_start_stall (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3330a8d33e08 Linux 5.15.201
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1381fffa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=e952109dd720d190f944
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b65fe19af112/disk-3330a8d3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/351948519a0d/vmlinux-3330a8d3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a3b3f8477595/bzImage-3330a8d3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e95210...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 5525 at kernel/rcu/tree_stall.h:937 rcu_check_gp_start_stall+0x2dc/0x460 kernel/rcu/tree_stall.h:929
Modules linked in:
CPU: 0 PID: 5525 Comm: syz.2.373 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:rcu_check_gp_start_stall+0x2dc/0x460 kernel/rcu/tree_stall.h:937
Code: ff ff ff 48 c7 c7 20 ec 31 96 be 04 00 00 00 e8 8a df 58 00 48 89 df b8 01 00 00 00 87 05 dc 9b cc 14 85 c0 0f 85 19 ff ff ff <0f> 0b 48 81 ff 00 2f 32 8c 74 47 48 c7 c0 c4 0f 8a 8d 48 c1 e8 03
RSP: 0018:ffffc90000007bb8 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffffffff8c322f00 RCX: ffffffff81655036
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8c322f00
RBP: ffffc90000007e10 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff2c63d84 R12: 0000000000002904
R13: ffff8880b903b258 R14: 0000000000000a02 R15: dffffc0000000000
FS: 00007f1abc30c6c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 000000004d6e9000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
rcu_core+0x62b/0x1670 kernel/rcu/tree.c:2758
handle_softirqs+0x339/0x830 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 ee ea 97 f7 48 89 df e8 26 c3 98 f7 e8 91 b5 b9 f7 fb bf 01 00 00 00 <e8> a6 c9 8c f7 65 8b 05 47 d7 3c 76 85 c0 74 02 5b c3 e8 94 e4 3a
RSP: 0018:ffffc9000335fbc0 EFLAGS: 00000282
RAX: b890a6cb6d220c00 RBX: ffff888073dd3780 RCX: b890a6cb6d220c00
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff888073dd3783 R09: 1ffff1100e7ba6f0
R10: dffffc0000000000 R11: ffffed100e7ba6f1 R12: ffff888073dd3780
R13: 0000000000000021 R14: dffffc0000000000 R15: 000000001c000004
spin_unlock_irq include/linux/spinlock.h:414 [inline]
get_signal+0x11d6/0x12c0 kernel/signal.c:2903
arch_do_signal_or_restart+0xe7/0x12c0 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f1abe0b2627
Code: 83 c8 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
RSP: 002b:00007f1abc30c028 EFLAGS: 00000246
RAX: 0000000000000048 RBX: 00007f1abe32bfa0 RCX: 00007f1abe0b2629
RDX: 0000200000000280 RSI: 0000000000000026 RDI: 0000000000000003
RBP: 00007f1abe148b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1abe32c038 R14: 00007f1abe32bfa0 R15: 00007ffcfbc75778
</TASK>
----------------
Code disassembly (best guess):
0: 00 00 add %al,(%rax)
2: 00 66 90 add %ah,-0x70(%rsi)
5: 53 push %rbx
6: 48 89 fb mov %rdi,%rbx
9: 48 83 c7 18 add $0x18,%rdi
d: 48 8b 74 24 08 mov 0x8(%rsp),%rsi
12: e8 ee ea 97 f7 call 0xf797eb05
17: 48 89 df mov %rbx,%rdi
1a: e8 26 c3 98 f7 call 0xf798c345
1f: e8 91 b5 b9 f7 call 0xf7b9b5b5
24: fb sti
25: bf 01 00 00 00 mov $0x1,%edi
* 2a: e8 a6 c9 8c f7 call 0xf78cc9d5 <-- trapping instruction
2f: 65 8b 05 47 d7 3c 76 mov %gs:0x763cd747(%rip),%eax # 0x763cd77d
36: 85 c0 test %eax,%eax
38: 74 02 je 0x3c
3a: 5b pop %rbx
3b: c3 ret
3c: e8 .byte 0xe8
3d: 94 xchg %eax,%esp
3e: e4 3a in $0x3a,%al


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