[syzbot] [kvm?] INFO: task hung in kvm_swap_active_memslots (2)

syzbot
2025-11-17T10:44:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 3a8660878839 Linux 6.18-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=160a05e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e854293d7f44b5a5
dashboard link: https://syzkaller.appspot.com/bug?extid=5c566b850d6ab6f0427a
compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/87a66406ce1a/disk-3a866087.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7c3300da5269/vmlinux-3a866087.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b4fcefdaf57b/bzImage-3a866087.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5c566b850d6ab6f0427a@syzkaller.appspotmail.com

INFO: task syz.2.1185:11790 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.1185 state:D stack:25976 pid:11790 tgid:11789 ppid:5836 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5325 [inline]
__schedule+0x1190/0x5de0 kernel/sched/core.c:6929
__schedule_loop kernel/sched/core.c:7011 [inline]
schedule+0xe7/0x3a0 kernel/sched/core.c:7026
kvm_swap_active_memslots+0x2ea/0x7d0 virt/kvm/kvm_main.c:1642
kvm_activate_memslot virt/kvm/kvm_main.c:1786 [inline]
kvm_create_memslot virt/kvm/kvm_main.c:1852 [inline]
kvm_set_memslot+0xd3b/0x1380 virt/kvm/kvm_main.c:1964
kvm_set_memory_region+0xe53/0x1610 virt/kvm/kvm_main.c:2120
kvm_set_internal_memslot+0x9f/0xe0 virt/kvm/kvm_main.c:2143
__x86_set_memory_region+0x2f6/0x740 arch/x86/kvm/x86.c:13242
kvm_alloc_apic_access_page+0xc5/0x140 arch/x86/kvm/lapic.c:2788
vmx_vcpu_create+0x503/0xbd0 arch/x86/kvm/vmx/vmx.c:7599
kvm_arch_vcpu_create+0x688/0xb20 arch/x86/kvm/x86.c:12706
kvm_vm_ioctl_create_vcpu virt/kvm/kvm_main.c:4207 [inline]
kvm_vm_ioctl+0xfec/0x3fd0 virt/kvm/kvm_main.c:5158
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3c9978eec9
RSP: 002b:00007f3c9a676038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3c999e5fa0 RCX: 00007f3c9978eec9
RDX: 0000000000000000 RSI: 000000000000ae41 RDI: 0000000000000003
RBP: 00007f3c99811f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3c999e6038 R14: 00007f3c999e5fa0 R15: 00007ffda33577e8
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
#0: ffffffff8e3c42e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8e3c42e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
#0: ffffffff8e3c42e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x36/0x1c0 kernel/locking/lockdep.c:6775
2 locks held by getty/8058:
#0: ffff88803440d0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
#1: ffffc9000e0cd2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x41b/0x14f0 drivers/tty/n_tty.c:2222
2 locks held by syz.2.1185/11790:
#0: ffff888032d640a8 (&kvm->slots_lock){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:228 [inline]
#0: ffff888032d640a8 (&kvm->slots_lock){+.+.}-{4:4}, at: kvm_alloc_apic_access_page+0x27/0x140 arch/x86/kvm/lapic.c:2782
#1: ffff888032d64138 (&kvm->slots_arch_lock){+.+.}-{4:4}, at: kvm_set_memslot+0x34/0x1380 virt/kvm/kvm_main.c:1915
4 locks held by kworker/u8:44/13722:
#0: ffff88801ba9f148 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3238
#1: ffffc9000b6cfd00 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3239
#2: ffffffff900e8630 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xad/0x8b0 net/core/net_namespace.c:669
#3: ffffffff8e3cf878 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock+0x1a3/0x3c0 kernel/rcu/tree_exp.h:343
4 locks held by syz-executor/14037:
#0: ffff888056654dc8 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_close+0x26/0x90 net/bluetooth/hci_core.c:499
#1: ffff8880566540b8 (&hdev->lock){+.+.}-{4:4}, at: hci_dev_close_sync+0x3ae/0x11d0 net/bluetooth/hci_sync.c:5291
#2: ffffffff90371248 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_disconn_cfm include/net/bluetooth/hci_core.h:2118 [inline]
#2: ffffffff90371248 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_conn_hash_flush+0xbb/0x260 net/bluetooth/hci_conn.c:2602
#3: ffff88803179c338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x80/0x730 net/bluetooth/l2cap_core.c:1762
1 lock held by syz.0.1905/15421:
#0: ffffffff900e8630 (pernet_ops_rwsem){++++}-{4:4}, at: copy_net_ns+0x2d6/0x690 net/core/net_namespace.c:576
1 lock held by syz.0.1905/15423:
#0: ffffffff900e8630 (pernet_ops_rwsem){++++}-{4:4}, at: copy_net_ns+0x2d6/0x690 net/core/net_namespace.c:576
2 locks held by syz.1.1908/15436:
#0: ffff88807a444dc8 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_close+0x26/0x90 net/bluetooth/hci_core.c:499
#1: ffff88807a4440b8 (&hdev->lock){+.+.}-{4:4}, at: hci_dev_close_sync+0x3ae/0x11d0 net/bluetooth/hci_sync.c:5291

=============================================

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
nmi_cpu_backtrace+0x27b/0x390 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x29c/0x300 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:332 [inline]
watchdog+0xf3f/0x1170 kernel/hung_task.c:495
kthread+0x3c5/0x780 kernel/kthread.c:463
ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

---
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