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

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+919877...@syzkaller.appspotmail.com
Tested-by: syzbot+919877...@syzkaller.appspotmail.com

Tested on:

commit: 230abd62 KVM: pfncache: Use a dedicated SRCU domain in..
git tree: git://git.infradead.org/users/dwmw2/linux.git xen-rcu-fixed
console output: https://syzkaller.appspot.com/x/log.txt?x=110522c6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9cef045500682f6b
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.
Note: testing is done by a robot and is best-effort only.

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to checkout kernel repo git://git.infradead.org/users/dwmw2/linux.git/xen-srcu-fixed: failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--force" "73b08201ab8ba1d188f45210a65f33cb30e5efaf" "xen-srcu-fixed"]: exit status 128


Tested on:

commit: [unknown
git tree: git://git.infradead.org/users/dwmw2/linux.git xen-srcu-fixed
kernel config: https://syzkaller.appspot.com/x/.config?x=a94030c847137a18

dashboard link: https://syzkaller.appspot.com/bug?extid=919877893c9d28162dc2
compiler:

[David Woodhouse]

On Mon, 2026-08-10 at 07:00 -0700, syzbot wrote:
> Hello,
>
> syzbot tried to test the proposed patch but the build/boot failed:
>
> failed to checkout kernel repo git://git.infradead.org/users/dwmw2/linux.git/xen-srcu-fixed: failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--force" "73b08201ab8ba1d188f45210a65f33cb30e5efaf" "xen-srcu-fixed"]: exit status 128

Huh, try again:

#syz test: git://git.infradead.org/users/dwmw2/linux.git xen-srcu-fixed

[Aleksandr Nogikh]

Hi David,

On Tue, Aug 11, 2026 at 9:52 AM David Woodhouse <dw...@infradead.org> wrote:
>
> On Mon, 2026-08-10 at 07:00 -0700, syzbot wrote:
> > Hello,
> >
> > syzbot tried to test the proposed patch but the build/boot failed:
> >
> > failed to checkout kernel repo git://git.infradead.org/users/dwmw2/linux.git/xen-srcu-fixed: failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--force" "73b08201ab8ba1d188f45210a65f33cb30e5efaf" "xen-srcu-fixed"]: exit status 128

FYI this seems like some syzbot infra problem, we are currently
looking into why this happened.

--
Aleksandr

>
> Huh, try again:
>
> #syz test: git://git.infradead.org/users/dwmw2/linux.git xen-srcu-fixed
>

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[David Woodhouse]

On Tue, 2026-08-11 at 10:58 +0200, Aleksandr Nogikh wrote:
> Hi David,
>
> On Tue, Aug 11, 2026 at 9:52 AM David Woodhouse <dw...@infradead.org>
> wrote:
> >
> > On Mon, 2026-08-10 at 07:00 -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot tried to test the proposed patch but the build/boot
> > > failed:
> > >
> > > failed to checkout kernel repo
> > > git://git.infradead.org/users/dwmw2/linux.git/xen-srcu-fixed:
> > > failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--
> > > force" "73b08201ab8ba1d188f45210a65f33cb30e5efaf" "xen-srcu-
> > > fixed"]: exit status 128
>
> FYI this seems like some syzbot infra problem, we are currently
> looking into why this happened.

No stderr from git in that report?

I suspect it could have been on my end. The bots around a way through
Anubis so the server was a bit slow to respond. Fixed now, so let's see
how the retry fares?

Thanks.

[Aleksandr Nogikh]

On Tue, Aug 11, 2026 at 2:12 PM David Woodhouse <dw...@infradead.org> wrote:
>
> On Tue, 2026-08-11 at 10:58 +0200, Aleksandr Nogikh wrote:
> > Hi David,
> >
> > On Tue, Aug 11, 2026 at 9:52 AM David Woodhouse <dw...@infradead.org>
> > wrote:
> > >
> > > On Mon, 2026-08-10 at 07:00 -0700, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot tried to test the proposed patch but the build/boot
> > > > failed:
> > > >
> > > > failed to checkout kernel repo
> > > > git://git.infradead.org/users/dwmw2/linux.git/xen-srcu-fixed:
> > > > failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--
> > > > force" "73b08201ab8ba1d188f45210a65f33cb30e5efaf" "xen-srcu-
> > > > fixed"]: exit status 128
> >
> > FYI this seems like some syzbot infra problem, we are currently
> > looking into why this happened.
>
> No stderr from git in that report?

It used to not print the git's stderr before :/
The latest revision should at least save it in the per-job log.

>
> I suspect it could have been on my end. The bots around a way through
> Anubis so the server was a bit slow to respond. Fixed now, so let's see
> how the retry fares?

That's good to know!
Yeah, let's try again.

>
> Thanks.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+919877...@syzkaller.appspotmail.com
Tested-by: syzbot+919877...@syzkaller.appspotmail.com

Tested on:

commit: bd0c3496 KVM: x86: Use gfn_to_pfn_cache for steal time..

git tree: git://git.infradead.org/users/dwmw2/linux.git xen-srcu-fixed

console output: https://syzkaller.appspot.com/x/log.txt?x=17dd3132580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9cef045500682f6b
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.

[syzbot]

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