Re: 2.6.29-rc3 circular locking dependency detected

[Avi Kivity <avi@redhat.com>]

Mark McLoughlin wrote:
> Hi,
>
> Just saw this when starting a guest with an assigned device.
>
> Cheers,
> Mark.
>
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.29-0.74.rc3.git3.fc11.x86_64 #1
> -------------------------------------------------------
> qemu-kvm/3706 is trying to acquire lock:
>  (&kvm->lock){--..}, at: [<ffffffffa013a25f>] kvm_emulate_pio+0x1ab/0x1ff [kvm]
>
> but task is already holding lock:
>  (&kvm->slots_lock){----}, at: [<ffffffffa013c4c0>] kvm_arch_vcpu_ioctl_run+0x49
> 7/0x73a [kvm]
>   

This is the expected nesting. kvm->slots_lock is outer to kvm->lock.

> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&kvm->slots_lock){----}:
>        [<ffffffff8106e9c1>] __lock_acquire+0xaab/0xc41
>        [<ffffffff8106ebe4>] lock_acquire+0x8d/0xba
>        [<ffffffff813826ae>] down_read+0x4b/0x7f
>        [<ffffffffa0137ff2>] kvm_iommu_map_guest+0x62/0xb8 [kvm]
>        [<ffffffffa01363ea>] kvm_vm_ioctl+0x3f4/0x7f1 [kvm]
>        [<ffffffff810eac30>] vfs_ioctl+0x2a/0x78
>        [<ffffffff810eb0e9>] do_vfs_ioctl+0x46b/0x4ab
>        [<ffffffff810eb17e>] sys_ioctl+0x55/0x77
>        [<ffffffff810112ba>] system_call_fastpath+0x16/0x1b
>        [<ffffffffffffffff>] 0xffffffffffffffff
>   

I think taking slots_lock in kvm_vm_ioctl_assign_device() (and dropping 
it from kvm_iommu_map_guest) should suffice, no?


-- 
error compiling committee.c: too many arguments to function