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

[Sean Christopherson]

On Fri, Sep 11, 2026, syzbot wrote:
> syzbot found the following issue on:
> 
> HEAD commit:    50d05c7c76c9 Merge tag 'landlock-7.3-rc3' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13db5ef9580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e
> dashboard link: https://syzkaller.appspot.com/bug?extid=ab6273c58262b9de56d9
> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=143121f9580000

The reproducer is "only" setting memory attributes on a 16MiB range.  I was
expecting a much, much larger range.  I suspect this one may be due to a problem
with the underlying GCE host?  Though it did spit out a reproducer...

> CPU: 1 UID: 0 PID: 6083 Comm: syz.4.24 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
> RIP: 0010:__this_cpu_preempt_check+0x0/0x20 lib/smp_processor_id.c:63
> Code: f5 48 8b 74 24 20 48 c7 c7 00 9b 6d 8c e8 88 ac 42 f5 e8 23 ab 4d f5 eb ae 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 48 89 fe 48 c7 c7 80 9a 6d 8c e9 0d ff ff ff cc cc cc
> RSP: 0018:ffffc90003d27460 EFLAGS: 00000046
> RAX: 0000000000000001 RBX: 0000000000000001 RCX: 8000000000000001
> RDX: 0000000000000000 RSI: ffff88807ea4a3d0 RDI: ffffffff8e6fe7fc
> RBP: 00000000ffffffff R08: ffffc90003d2755f R09: 0000000000000000
> R10: ffffc90003d27548 R11: fffff520007a4eac R12: 0000000000000246
> R13: ffff8880314c5dc0 R14: ffff88807ea4a3d0 R15: 0000000000000001
> FS:  0000000000000000(0000) GS:ffff888124dd2000(0063) knlGS:00000000f6834b40
> CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 00000000f71e8c10 CR3: 0000000073d5a000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  lockdep_recursion_finish kernel/locking/lockdep.c:470 [inline]
>  lock_is_held_type+0xdf/0x150 kernel/locking/lockdep.c:6017
>  lock_is_held include/linux/lockdep.h:249 [inline]
>  xa_entry include/linux/xarray.h:1227 [inline]
>  xas_descend lib/xarray.c:208 [inline]
>  xas_load+0x198/0x5a0 lib/xarray.c:246
>  __xa_cmpxchg_raw lib/xarray.c:1783 [inline]
>  __xa_cmpxchg+0xc3/0x1f0 lib/xarray.c:1769
>  xa_cmpxchg include/linux/xarray.h:699 [inline]
>  xa_reserve include/linux/xarray.h:1088 [inline]
>  kvm_vm_set_mem_attributes virt/kvm/kvm_main.c:2577 [inline]
>  kvm_vm_ioctl_set_mem_attributes+0x429/0x1600 virt/kvm/kvm_main.c:2625
>  kvm_vm_ioctl+0xb33/0xd30 virt/kvm/kvm_main.c:5356
>  kvm_vm_compat_ioctl+0x2b1/0x3a0 virt/kvm/kvm_main.c:5480
>  __do_compat_sys_ioctl fs/ioctl.c:695 [inline]
>  __se_compat_sys_ioctl fs/ioctl.c:638 [inline]
>  __ia32_compat_sys_ioctl+0x5ea/0x950 fs/ioctl.c:638
>  do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
>  __do_fast_syscall_32+0x27a/0x6a0 arch/x86/entry/syscall_32.c:291
>  do_fast_syscall_32+0x33/0x70 arch/x86/entry/syscall_32.c:316
>  entry_SYSENTER_compat_after_hwframe+0x84/0x8e
> RIP: 0023:0xf705f0ec
> Code: 90 85 d2 74 0a 89 ce 81 e6 ff 0f 00 00 89 32 85 c0 74 05 c1 e9 0c 89 08 31 c0 5e 5d c3 90 0f 1f 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 58 b8
> RSP: 002b:00000000f683450c EFLAGS: 00000206 ORIG_RAX: 0000000000000036
> RAX: ffffffffffffffda RBX: 0000000000000007 RCX: 000000004020aed2
> RDX: 0000000080000200 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>