Re: WARNING in __mutex_unlock_slowpath

[Paolo Bonzini]

On 29/04/2018 19:00, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on upstream commit
> bf8f5de17442bba5f811e7e724980730e079ee11 (Sat Apr 28 17:05:04 2018 +0000)
> MAINTAINERS: add myself as maintainer of AFFS
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=35666cba7f0a337e2e79
> 
> C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5686569910403072
> syzkaller reproducer:
> https://syzkaller.appspot.com/x/repro.syz?id=5767017265102848
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=6346308495343616
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=7043958930931867332
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+35666cba7f0a337e2e79@xxxxxxxxxxxxxxxxxxxxxxxxx
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.
> 
> ------------[ cut here ]------------
> DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current)
> WARNING: CPU: 0 PID: 4525 at kernel/locking/mutex.c:1032
> __mutex_unlock_slowpath+0x62e/0x8a0 kernel/locking/mutex.c:1032
> Kernel panic - not syncing: panic_on_warn set ...

This doesn't make much sense, unless it's a "generic" memory corruption,
but at least the reproducer seems to be simple, just (in pseudocode)

  ioctl(kvm_vm_fd, KVM_HYPERV_EVENTFD,
        { fd = some_eventfd, conn_id = 0, flags = 0 })
  ioctl(kvm_vm_fd, KVM_HYPERV_EVENTFD,
        { fd = -1, conn_id = 5, flags = KVM_HYPERV_EVENTFD_DEASSIGN })

Roman, Cathy, can you give it a quick look?  (Reproducing the reproducer
link: https://syzkaller.appspot.com/x/repro.c?id=5686569910403072).

Paolo

> CPU: 0 PID: 4525 Comm: syz-executor809 Not tainted 4.17.0-rc2+ #22
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> Â__dump_stack lib/dump_stack.c:77 [inline]
> Âdump_stack+0x1b9/0x294 lib/dump_stack.c:113
> Âpanic+0x22f/0x4de kernel/panic.c:184
> Â__warn.cold.8+0x163/0x1b3 kernel/panic.c:536
> Âreport_bug+0x252/0x2d0 lib/bug.c:186
> Âfixup_bug arch/x86/kernel/traps.c:178 [inline]
> Âdo_error_trap+0x1de/0x490 arch/x86/kernel/traps.c:296
> Âdo_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
> Âinvalid_op+0x14/0x20 arch/x86/entry/entry_64.S:992
> RIP: 0010:__mutex_unlock_slowpath+0x62e/0x8a0 kernel/locking/mutex.c:1032
> RSP: 0018:ffff8801cf31f138 EFLAGS: 00010286
> RAX: 0000000000000033 RBX: 1ffff10039e63e30 RCX: ffffffff8160b82d
> RDX: 0000000000000000 RSI: ffffffff816104e1 RDI: 0000000000000001
> RBP: ffff8801cf31f2a8 R08: ffff8801d9042180 R09: fffffbfff11b0974
> R10: fffffbfff11b0974 R11: ffffffff88d84ba3 R12: ffffffff8a713a20
> R13: dffffc0000000000 R14: 0000000000000000 R15: ffff8801989d6b08
> Âmutex_unlock+0xd/0x10 kernel/locking/mutex.c:614
> Âkvm_hv_eventfd_deassign arch/x86/kvm/hyperv.c:1434 [inline]
> Âkvm_vm_ioctl_hv_eventfd+0x1ea/0x24b arch/x86/kvm/hyperv.c:1451
> Âkvm_arch_vm_ioctl+0x155e/0x2690 arch/x86/kvm/x86.c:4563
> Âkvm_vm_ioctl+0x246/0x1d90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3100
> Âvfs_ioctl fs/ioctl.c:46 [inline]
> Âfile_ioctl fs/ioctl.c:500 [inline]
> Âdo_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
> Âksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
> Â__do_sys_ioctl fs/ioctl.c:708 [inline]
> Â__se_sys_ioctl fs/ioctl.c:706 [inline]
> Â__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
> Âdo_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> Âentry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4401f9
> RSP: 002b:00007ffcd5727a48 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 6d766b2f7665642f RCX: 00000000004401f9
> RDX: 0000000020000140 RSI: 000000004018aebd RDI: 00000000000000ee
> RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
> R10: 00000000004002c8 R11: 0000000000000217 R12: 0000000000401720
> R13: 00000000004017b0 R14: 0000000000000000 R15: 0000000000000000
> Dumping ftrace buffer:
> ÂÂ (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
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