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

[Alexander Graf]

On 16.11.2013, at 01:55, Paul Mackerras <paulus at samba.org> wrote:

> On Fri, Nov 15, 2013 at 04:35:00PM +0800, Liu Ping Fan 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>
> 
> Reviewed-by: Paul Mackerras <paulus at samba.org>

Thanks, applied to kvm-ppc-queue.


Alex