Re: [Xen-devel] [PATCHv11 2/4] gnttab: introduce maptrack lock

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 05/06/15 15:38, Jan Beulich wrote:
>>>> On 05.06.15 at 15:44, <david.vrabel@xxxxxxxxxx> wrote:
>> On 05/06/15 14:35, Jan Beulich wrote:
>>>>>> On 02.06.15 at 18:26, <david.vrabel@xxxxxxxxxx> wrote:
>>>> --- a/xen/common/grant_table.c
>>>> +++ b/xen/common/grant_table.c
>>>> @@ -288,10 +288,10 @@ static inline void put_maptrack_handle(
>>>>      struct grant_table *t, int handle)
>>>>  {
>>>> -    spin_lock(&t->lock);
>>>> +    spin_lock(&t->maptrack_lock);
>>>>      maptrack_entry(t, handle).ref = t->maptrack_head;
>>>>      t->maptrack_head = handle;
>>>> -    spin_unlock(&t->lock);
>>>> +    spin_unlock(&t->maptrack_lock);
>>>
>>> Starting with this change it becomes unclear what protects the
>>> maptrack entries - the grant table lock or the maptrack one?
>>
>> The grant table lock.  The docs aren't very good here -- the maptrack
>> lock is only for the maptrack free list.
> 
> I don't think the grant table lock serves that purpose, at least not
> anymore after being converted to RW. See my reply on patch 3.

Sorry for not being clear, after this patch #2 it is the grant table
lock that serves this purpose.  After #3 it's as you said there.

David

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