Re: [syzbot] [kvm-x86?] [kvm?] WARNING: locking bug in kvm_xen_set_evtchn_fast

[syzbot <syzbot+919877893c9d28162dc2@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: locking bug in kvm_xen_set_evtchn_fast

=============================
[ BUG: Invalid wait context ]
syzkaller #0 Not tainted
-----------------------------
swapper/0/0 is trying to lock:
ffff8880364ed370 (&gpc->lock){....}-{3:3}, at: kvm_xen_set_evtchn_fast+0x1f4/0x9a0 arch/x86/kvm/xen.c:1822
other info that might help us debug this:
context-{2:2}
1 lock held by swapper/0/0:
 #0: ffff8880364ed8d0 (&kvm->srcu){.?.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:187 [inline]
 #0: ffff8880364ed8d0 (&kvm->srcu){.?.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:294 [inline]
 #0: ffff8880364ed8d0 (&kvm->srcu){.?.+}-{0:0}, at: kvm_xen_set_evtchn_fast+0x1bc/0x9a0 arch/x86/kvm/xen.c:1820
stack backtrace:
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_lock_invalid_wait_context kernel/locking/lockdep.c:4830 [inline]
 check_wait_context kernel/locking/lockdep.c:4902 [inline]
 __lock_acquire+0xe39/0x2cf0 kernel/locking/lockdep.c:5187
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __raw_read_lock_irqsave include/linux/rwlock_api_smp.h:174 [inline]
 _raw_read_lock_irqsave+0x48/0x60 kernel/locking/spinlock.c:240
 kvm_xen_set_evtchn_fast+0x1f4/0x9a0 arch/x86/kvm/xen.c:1822
 xen_timer_callback+0x109/0x220 arch/x86/kvm/xen.c:140
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x371/0xa10 kernel/time/hrtimer.c:2096
 hrtimer_interrupt+0x448/0x910 kernel/time/hrtimer.c:2215
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x102/0x430 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: 2c 64 02 e9 83 02 03 00 cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 23 5a 14 00 fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
RSP: 0018:ffffffff8e207de0 EFLAGS: 00000246
RAX: 00000000000ce103 RBX: ffffffff81994630 RCX: 0000000080000001
RDX: 0000000000000001 RSI: ffffffff8dcc8ad1 RDI: ffffffff8c038b80
RBP: ffffffff8e207eb8 R08: ffff8880b86338db R09: 1ffff110170c671b
R10: dffffc0000000000 R11: ffffed10170c671c R12: 0000000000000000
R13: 1ffffffff1c51dd8 R14: 1ffffffff1c40fc4 R15: dffffc0000000000
 arch_safe_halt arch/x86/kernel/process.c:767 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:768
 default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x2e0/0x540 kernel/sched/idle.c:355
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:454
 rest_init+0x2de/0x300 init/main.c:717
 start_kernel+0x392/0x3e0 init/main.c:1175
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x137/0x1b0 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x157
 </TASK>
----------------
Code disassembly (best guess):
   0:	2c 64                	sub    $0x64,%al
   2:	02 e9                	add    %cl,%ch
   4:	83 02 03             	addl   $0x3,(%rdx)
   7:	00 cc                	add    %cl,%ah
   9:	cc                   	int3
   a:	cc                   	int3
   b:	90                   	nop
   c:	90                   	nop
   d:	90                   	nop
   e:	90                   	nop
   f:	90                   	nop
  10:	90                   	nop
  11:	90                   	nop
  12:	90                   	nop
  13:	90                   	nop
  14:	90                   	nop
  15:	90                   	nop
  16:	90                   	nop
  17:	90                   	nop
  18:	90                   	nop
  19:	90                   	nop
  1a:	90                   	nop
  1b:	f3 0f 1e fa          	endbr64
  1f:	66 90                	xchg   %ax,%ax
  21:	0f 00 2d 23 5a 14 00 	verw   0x145a23(%rip)        # 0x145a4b
  28:	fb                   	sti
  29:	f4                   	hlt
* 2a:	c3                   	ret <-- trapping instruction
  2b:	cc                   	int3
  2c:	cc                   	int3
  2d:	cc                   	int3
  2e:	cc                   	int3
  2f:	cc                   	int3
  30:	cc                   	int3
  31:	cc                   	int3
  32:	cc                   	int3
  33:	cc                   	int3
  34:	cc                   	int3
  35:	cc                   	int3
  36:	cc                   	int3
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	90                   	nop
  3c:	90                   	nop
  3d:	90                   	nop
  3e:	90                   	nop
  3f:	90                   	nop


Tested on:

commit:         d58772d8 Merge tag 'regmap-fix-v7.2-rc7' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10851079580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c9e57f4ebf5743f1
dashboard link: https://syzkaller.appspot.com/bug?extid=919877893c9d28162dc2
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Note: no patches were applied.