Re: WARNING: suspicious RCU usage in kvm_dev_ioctl

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    9d234505 Merge tag 'hwmon-for-v5.4-rc6' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15bf068ae00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cbbed3e8d4eb64bf
dashboard link: https://syzkaller.appspot.com/bug?extid=75475908cd0910f141ee
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e20268e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15209b84e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+75475908cd0910f141ee@xxxxxxxxxxxxxxxxxxxxxxxxx

=============================
WARNING: suspicious RCU usage
5.4.0-rc5+ #0 Not tainted
-----------------------------
include/linux/kvm_host.h:534 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
no locks held by syz-executor978/9604.

stack backtrace:
CPU: 0 PID: 9604 Comm: syz-executor978 Not tainted 5.4.0-rc5+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 lockdep_rcu_suspicious+0x153/0x15d kernel/locking/lockdep.c:5438
 kvm_get_bus include/linux/kvm_host.h:534 [inline]
 kvm_get_bus include/linux/kvm_host.h:532 [inline]
 kvm_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:706 [inline]
 kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3444  
[inline]
 kvm_dev_ioctl+0x100c/0x1610 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3496
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441159
Code: e8 fc ab 02 00 48 83 c4 18 c3 0f 1f 80 00 00 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 0f 83 9b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdef5e0888 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441159
RDX: 0000000000000002 RSI: 000000000000ae01 RDI: 0000000000000003
RBP: 00000000006cb018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000401f80
R13: 0000000000402010 R14: 0000000000000000 R15: 0000000000000000

=============================
WARNING: suspicious RCU usage
5.4.0-rc5+ #0 Not tainted
-----------------------------
include/linux/kvm_host.h:629 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
no locks held by syz-executor978/9604.

stack backtrace:
CPU: 0 PID: 9604 Comm: syz-executor978 Not tainted 5.4.0-rc5+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 lockdep_rcu_suspicious+0x153/0x15d kernel/locking/lockdep.c:5438
 __kvm_memslots include/linux/kvm_host.h:629 [inline]
 __kvm_memslots include/linux/kvm_host.h:626 [inline]
 kvm_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:708 [inline]
 kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3444  
[inline]
 kvm_dev_ioctl+0x116c/0x1610 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3496
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441159
Code: e8 fc ab 02 00 48 83 c4 18 c3 0f 1f 80 00 00 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 0f 83 9b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdef5e0888 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441159
RDX: 0000000000000002 RSI: 000000000000ae01 RDI: 0000000000000003
RBP: 00000000006cb018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000401f80
R13: 0000000000402010 R14: 0000000000000000 R15: 0000000000000000