[PATCH RESEND v4] powerpc: kvm: fix rare but potential deadlock scene

[Liu ping fan]

On Tue, Nov 19, 2013 at 6:39 PM, Alexander Graf <agraf at suse.de> wrote:
>
> On 19.11.2013, at 07:12, Liu Ping Fan <kernelfans at gmail.com> wrote:
>
>> Since kvmppc_hv_find_lock_hpte() is called from both virtmode and
>> realmode, so it can trigger the deadlock.
>>
>> Suppose the following scene:
>>
>> Two physical cpuM, cpuN, two VM instances A, B, each VM has a group of
>> vcpus.
>>
>> If on cpuM, vcpu_A_1 holds bitlock X (HPTE_V_HVLOCK), then is switched
>> out, and on cpuN, vcpu_A_2 try to lock X in realmode, then cpuN will be
>> caught in realmode for a long time.
>>
>> What makes things even worse if the following happens,
>>  On cpuM, bitlockX is hold, on cpuN, Y is hold.
>>  vcpu_B_2 try to lock Y on cpuM in realmode
>>  vcpu_A_2 try to lock X on cpuN in realmode
>>
>> Oops! deadlock happens
>>
>> Signed-off-by: Liu Ping Fan <pingfank at linux.vnet.ibm.com>
>
> Any particular reason for the resend? The patch is already applied, no?
>
Oh, seems that I misunderstood your meaning. You said "Actually, I've
changed my mind and moved the patch to the for-3.13 branch instead.
Please make sure to CC kvm at vger on all patches you submit though". So
I think it is necessary to resend with cc kvm at vger

Regards,
Pingfan