linux-kernel - [syzbot] [kvm?] [kvm-x86?] INFO: rcu detected stall in kvm_vcpu

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Message-ID: <694f53ba.050a0220.35954c.0084.GAE@google.com>
Date: Fri, 26 Dec 2025 19:34:18 -0800
From: syzbot <syzbot+3d5461510f8dc4adfe30@...kaller.appspotmail.com>
To: bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mingo@...hat.com, 
	pbonzini@...hat.com, seanjc@...gle.com, syzkaller-bugs@...glegroups.com, 
	tglx@...utronix.de, vkuznets@...hat.com, x86@...nel.org
Subject: [syzbot] [kvm?] [kvm-x86?] INFO: rcu detected stall in kvm_vcpu_ioctl (4)

Hello,

syzbot found the following issue on:

HEAD commit:    cc3aa43b44bd Add linux-next specific files for 20251219
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1252109a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f7a09bf3b9133d9d
dashboard link: https://syzkaller.appspot.com/bug?extid=3d5461510f8dc4adfe30
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14eb1022580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13cc18fc580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b1b23d9783ee/disk-cc3aa43b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/07451939cf74/vmlinux-cc3aa43b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e5ddf385746f/bzImage-cc3aa43b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3d5461510f8dc4adfe30@...kaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	(detected by 1, t=10502 jiffies, g=14269, q=1142 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10500 (4294965239-4294954739), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10500 jiffies! g14269 f0x2 RCU_GP_WAIT_FQS(5) ->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:27128 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5258 [inline]
 __schedule+0x150e/0x5070 kernel/sched/core.c:6866
 __schedule_loop kernel/sched/core.c:6948 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6963
 schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6253 Comm: syz.1.63 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:_raw_spin_unlock_irqrestore+0x4b/0x110 kernel/locking/spinlock.c:193
Code: fb 60 5a 07 48 89 44 24 48 48 c7 04 24 b3 8a b5 41 48 c7 44 24 08 96 3d b2 8d 48 c7 44 24 10 00 df 69 8b 49 89 e7 49 c1 ef 03 <48> b8 f1 f1 f1 f1 00 f3 f3 f3 49 bc 00 00 00 00 00 fc ff df 4b 89
RSP: 0018:ffffc90000007ca0 EFLAGS: 00000802
RAX: 5de15cb931505900 RBX: 0000000000000806 RCX: ffff88802eff1e80
RDX: 0000000000010000 RSI: 0000000000000806 RDI: ffff8880b8628240
RBP: ffffc90000007d30 R08: ffffffff8fc3d077 R09: 1ffffffff1f87a0e
R10: dffffc0000000000 R11: fffffbfff1f87a0f R12: ffff888078156180
R13: dffffc0000000000 R14: ffff8880b8628240 R15: 1ffff92000000f94
FS:  00007f635365c6c0(0000) GS:ffff8881259dc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31363fff CR3: 000000004c992000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 __run_hrtimer kernel/time/hrtimer.c:1773 [inline]
 __hrtimer_run_queues+0x408/0xc30 kernel/time/hrtimer.c:1841
 hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1903
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1045 [inline]
 __sysvec_apic_timer_interrupt+0x102/0x3e0 arch/x86/kernel/apic/apic.c:1062
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1056
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa8/0x110 kernel/locking/spinlock.c:194
Code: 74 05 e8 0b f4 5f f6 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4f f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 23 6b 27 f6 65 8b 05 7c 60 5a 07 85 c0 74 40 48 c7 04 24 0e 36
RSP: 0018:ffffc900040a7320 EFLAGS: 00000206
RAX: 5de15cb931505900 RBX: 0000000000000a06 RCX: 5de15cb931505900
RDX: 0000000000000007 RSI: ffffffff8daa9dc3 RDI: 0000000000000001
RBP: ffffc900040a73b0 R08: ffffffff8fc3d077 R09: 1ffffffff1f87a0e
R10: dffffc0000000000 R11: fffffbfff1f87a0f R12: dffffc0000000000
R13: 0000000000000000 R14: ffff8880b8628240 R15: 1ffff92000814e64
 hrtimer_start include/linux/hrtimer.h:259 [inline]
 stimer_start arch/x86/kvm/hyperv.c:682 [inline]
 kvm_hv_process_stimers+0xd0a/0x16a0 arch/x86/kvm/hyperv.c:893
 vcpu_enter_guest arch/x86/kvm/x86.c:11193 [inline]
 vcpu_run+0x2240/0x76b0 arch/x86/kvm/x86.c:11639
 kvm_arch_vcpu_ioctl_run+0x1148/0x1c90 arch/x86/kvm/x86.c:11984
 kvm_vcpu_ioctl+0x99a/0xed0 virt/kvm/kvm_main.c:4492
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f635278f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f635365c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f63529e5fa0 RCX: 00007f635278f749
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
RBP: 00007f6352813f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f63529e6038 R14: 00007f63529e5fa0 R15: 00007ffd5b219358
 </TASK>


---
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