syzbot
WARNING in rcu_check_gp_start_stall (4)
Status:
upstream: reported on 2026/02/20 21:56
Reported-by: syzbot+e952109dd720d190f944@syzkaller.appspotmail.com
First crash: 154d, last: 7d11h
Sample crash report:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 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: 0 Comm: swapper/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
RIP: 0010:rcu_check_gp_start_stall+0x2dc/0x460 kernel/rcu/tree_stall.h:937
Code: ff ff ff 48 c7 c7 20 4c 33 96 be 04 00 00 00 e8 4a f6 58 00 48 89 df b8 01 00 00 00 87 05 9c 2f ce 14 85 c0 0f 85 19 ff ff ff <0f> 0b 48 81 ff 80 33 32 8c 74 47 48 c7 c0 84 1e 8b 8d 48 c1 e8 03
RSP: 0018:ffffc90000007bd8 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffffffff8c323380 RCX: ffffffff81651c76
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8c323380
RBP: ffffc90000007e10 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff2c66984 R12: 0000000000002904
R13: dffffc0000000000 R14: 0000000000000a02 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0177f9e580 CR3: 00000000486a2000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
rcu_core+0x631/0x1650 kernel/rcu/tree.c:2758
handle_softirqs+0x336/0x830 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:default_idle+0xb/0x10 arch/x86/kernel/process.c:730
Code: b7 48 89 df e8 56 a7 f5 f7 eb ad e8 3f ac f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 cc 66 90 0f 00 2d 57 64 5d 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffffff8c007dc8 EFLAGS: 000002c6
RAX: 4ac790015fb92300 RBX: ffffffff8c0bc480 RCX: 4ac790015fb92300
RDX: 0000000000000001 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a2a40
RBP: ffffffff8c007ef8 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: 1ffffffff1800fc4
R13: dffffc0000000000 R14: 1ffffffff1817890 R15: 0000000000000000
default_idle_call+0x81/0xc0 kernel/sched/idle.c:112
cpuidle_idle_call kernel/sched/idle.c:202 [inline]
do_idle+0x3a1/0x650 kernel/sched/idle.c:326
cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:424
start_kernel+0x489/0x540 init/main.c:1153
secondary_startup_64_no_verify+0xb1/0xbb
</TASK>
----------------
Code disassembly (best guess):
0: b7 48 mov $0x48,%bh
2: 89 df mov %ebx,%edi
4: e8 56 a7 f5 f7 call 0xf7f5a75f
9: eb ad jmp 0xffffffb8
b: e8 3f ac f6 ff call 0xfff6ac4f
10: 00 00 add %al,(%rax)
12: cc int3
13: cc int3
14: 00 00 add %al,(%rax)
16: cc int3
17: cc int3
18: 00 00 add %al,(%rax)
1a: cc int3
1b: cc int3
1c: 00 00 add %al,(%rax)
1e: cc int3
1f: 66 90 xchg %ax,%ax
21: 0f 00 2d 57 64 5d 00 verw 0x5d6457(%rip) # 0x5d647f
28: fb sti
29: f4 hlt
* 2a: c3 ret <-- trapping instruction
2b: 0f 1f 40 00 nopl 0x0(%rax)
2f: 41 57 push %r15
31: 41 56 push %r14
33: 53 push %rbx
34: 49 be 00 00 00 00 00 movabs $0xdffffc0000000000,%r14
3b: fc ff df
3e: 65 gs
3f: 48 rex.W
* Struck through repros no longer work on HEAD.