From: syzbot ci <syzbot+ci189dc6e331dcf349@syzkaller.appspotmail.com>
To: dwmw2@infradead.org, dwmw@amazon.co.uk, fgriffo@amazon.co.uk,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, paul@xen.org,
pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com
Cc: syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com
Subject: [syzbot ci] Re: KVM: x86/xen: Don't drop event deliveries which race memslot updates
Date: Wed, 14 Oct 2026 23:31:47 -0700 [thread overview]
Message-ID: <6ad07353.5f317f00.247b6.0062.GAE@google.com> (raw)
In-Reply-To: <20261014220508.518772-1-dwmw2@infradead.org>
syzbot ci has tested the following series
[v2] KVM: x86/xen: Don't drop event deliveries which race memslot updates
https://lore.kernel.org/all/20261014220508.518772-1-dwmw2@infradead.org
* [PATCH v2 01/11] KVM: pfncache: Return -EAGAIN for a lookup which hits an invalid memslot
* [PATCH v2 02/11] KVM: pfncache: Add a 'wait' argument to the refresh and activate functions
* [PATCH v2 03/11] KVM: x86/xen: Don't block on xen_lock within the vCPU's kvm->srcu section
* [PATCH v2 04/11] KVM: x86/xen: Wait out memslot updates in the Xen attribute ioctls
* [PATCH v2 05/11] KVM: x86/xen: Don't lose the timer event when delivery fails transiently
* [PATCH v2 06/11] KVM: x86/xen: Retry event channel delivery which races a memslot update
* [PATCH v2 07/11] KVM: x86/xen: Extract delivery of event to vCPU into a separate helper
* [PATCH v2 08/11] KVM: x86/xen: Explicitly tag "shared info" page as never being dirty tracked
* [PATCH v2 09/11] KVM: x86/xen: Don't dirty track "vCPU info" page
* [PATCH v2 10/11] KVM: x86: Request the guest TLB flush from record_steal_time()
* [PATCH v2 11/11] KVM: selftests: Add Xen evtchn vs memslot-update race test
and found the following issue:
WARNING: suspicious RCU usage in kvm_gpc_check
Full report is available here:
https://ci.syzbot.org/series/cde10220-9f8c-48fe-a62d-36d3df4d9a0b
***
WARNING: suspicious RCU usage in kvm_gpc_check
tree: kvm-next
URL: https://kernel.googlesource.com/pub/scm/virt/kvm/kvm/
base: d4b7fb647204f0c81dfeae2d1a708e4d858e0c94
arch: amd64
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config: https://ci.syzbot.org/builds/dbdeec8a-a092-44d6-96b1-12ae99a6a0ce/config
=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
./include/linux/kvm_host.h:1094 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
locks held by syz.0.18064/14640: 3, last CPU#0:
#0: ffff8881133851a8 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x27f/0xfd0
#1: ffff8880201d5d30 (&kvm->arch.xen.xen_lock){+.+.}-{4:4}, at: kvm_xen_vcpu_set_attr+0x4d/0x1250
#2: ffff8881133861e0 (&gpc->lock){....}-{3:3}, at: xen_get_guest_pvclock+0x29/0x260
stack backtrace:
CPU: 0 UID: 0 PID: 14640 Comm: syz.0.18064 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150
lockdep_rcu_suspicious+0x140/0x1d0
kvm_gpc_check+0x325/0x380
xen_get_guest_pvclock+0x3e/0x260
kvm_xen_start_timer+0x160/0x5f0
kvm_xen_vcpu_set_attr+0xbb2/0x1250
kvm_arch_vcpu_ioctl+0x1485/0x23a0
kvm_vcpu_ioctl+0x7e3/0xfd0
__se_sys_ioctl+0xfc/0x170
do_syscall_64+0x166/0x520
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3c49f9e559
Code: 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 01 48
RSP: 002b:00007f3c4ae4a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3c4a226090 RCX: 00007f3c49f9e559
RDX: 00002000000000c0 RSI: 000000004048aecb RDI: 000000000000000a
RBP: 00007f3c4a0358b0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3c4a226128 R14: 00007f3c4a226090 R15: 00007ffed7dff5b8
</TASK>
***
If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com
---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.
To test a fix for this bug, please reply with `#syz test`
(on a separate line) and attach the patch to the email.
Notes:
- The patch will be applied on top of the tested series (as an
incremental fix).
- To test a new version of the whole series, please send it directly
to syzbot@lists.linux.dev.
- Arguments like custom git repos and branches are not supported.
prev parent reply other threads:[~2026-10-15 6:31 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-14 22:04 [PATCH v2 00/11] " David Woodhouse
2026-10-14 22:04 ` [PATCH v2 01/11] KVM: pfncache: Return -EAGAIN for a lookup which hits an invalid memslot David Woodhouse
2026-10-14 22:04 ` [PATCH v2 02/11] KVM: pfncache: Add a 'wait' argument to the refresh and activate functions David Woodhouse
2026-10-14 22:04 ` [PATCH v2 03/11] KVM: x86/xen: Don't block on xen_lock within the vCPU's kvm->srcu section David Woodhouse
2026-10-14 22:05 ` [PATCH v2 04/11] KVM: x86/xen: Wait out memslot updates in the Xen attribute ioctls David Woodhouse
2026-10-14 22:05 ` [PATCH v2 05/11] KVM: x86/xen: Don't lose the timer event when delivery fails transiently David Woodhouse
2026-10-14 22:05 ` [PATCH v2 06/11] KVM: x86/xen: Retry event channel delivery which races a memslot update David Woodhouse
2026-10-14 22:05 ` [PATCH v2 07/11] KVM: x86/xen: Extract delivery of event to vCPU into a separate helper David Woodhouse
2026-10-14 22:05 ` [PATCH v2 08/11] KVM: x86/xen: Explicitly tag "shared info" page as never being dirty tracked David Woodhouse
2026-10-14 22:05 ` [PATCH v2 09/11] KVM: x86/xen: Don't dirty track "vCPU info" page David Woodhouse
2026-10-14 22:05 ` [PATCH v2 10/11] KVM: x86: Request the guest TLB flush from record_steal_time() David Woodhouse
2026-10-14 22:05 ` [PATCH v2 11/11] KVM: selftests: Add Xen evtchn vs memslot-update race test David Woodhouse
2026-10-15 6:31 ` syzbot ci [this message]
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