suspicious RCU usage with kvm_pr

[Denis Kirjanov]

On 9/16/15, Thomas Huth <thuth at redhat.com> wrote:
> On 16/09/15 10:51, Denis Kirjanov wrote:
>> Hi,
>>
>> I see the following trace on qemu startup (ps700 blade):
>>
>> v4.2-11169-g64d1def
>>
>>
>> [  143.369638] ===============================
>> [  143.369640] [ INFO: suspicious RCU usage. ]
>> [  143.369643] 4.2.0-11169-g64d1def #10 Tainted: G S
>> [  143.369645] -------------------------------
>> [  143.369647] arch/powerpc/kvm/../../../virt/kvm/kvm_main.c:3310
>> suspicious rcu_dereference_check() usage!
>> [  143.369649]
>> other info that might help us debug this:
>>
>> [  143.369652]
>> rcu_scheduler_active = 1, debug_locks = 1
>> [  143.369655] 1 lock held by qemu-system-ppc/2292:
>> [  143.369656]  #0:  (&vcpu->mutex){+.+.+.}, at: [<d000000004225bac>]
>> .vcpu_load+0x2c/0xb0 [kvm]
>> [  143.369672]
>> stack backtrace:
>> [  143.369675] CPU: 12 PID: 2292 Comm: qemu-system-ppc Tainted: G S
>>           4.2.0-11169-g64d1def #10
>> [  143.369677] Call Trace:
>> [  143.369682] [c0000001d08bf200] [c000000000816dd0]
>> .dump_stack+0x98/0xd4 (unreliable)
>> [  143.369687] [c0000001d08bf280] [c0000000000f7058]
>> .lockdep_rcu_suspicious+0x108/0x170
>> [  143.369696] [c0000001d08bf310] [d0000000042296d8]
>> .kvm_io_bus_read+0x1d8/0x220 [kvm]
>> [  143.369705] [c0000001d08bf3c0] [d00000000422f980]
>> .kvmppc_h_logical_ci_load+0x60/0xe0 [kvm]
>
> Could it be that we need to srcu_read_lock(&vcpu->kvm->srcu) before
> calling the kvm_io_bus_read/write() function in the
> kvmppc_h_logical_ci_load/store() function?

I haven't had time to dig into this. I'll try it.

Thanks

>
>  Thomas
>
>