Re: [PATCH v6 03/13] vpci: move lock outside of struct vpci

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 07.02.22 16:11, Jan Beulich wrote:
> On 07.02.2022 14:53, Oleksandr Andrushchenko wrote:
>> On 07.02.22 14:46, Roger Pau Monné wrote:
>>> I think the per-domain rwlock seems like a good option. I would do
>>> that as a pre-patch.
>> It is. But it seems it won't solve the thing we started this adventure for:
>>
>> With per-domain read lock and still ABBA in modify_bars (hope the below
>> is correctly seen with a monospace font):
>>
>> cpu0: vpci_write-> d->RLock -> pdev1->lock ->                                
>>                   rom_write -> modify_bars: tmp (pdev2) ->lock
>> cpu1:        vpci_write-> d->RLock pdev2->lock -> cmd_write -> modify_bars: 
>> tmp (pdev1) ->lock
>>
>> There is no API to upgrade read lock to write lock in modify_bars which 
>> could help,
>> so in both cases vpci_write should take write lock.
> Hmm, yes, I think you're right: It's not modify_bars() itself which needs
> to acquire the write lock, but its (perhaps indirect) caller. Effectively
> vpci_write() would need to take the write lock if the range written
> overlaps the BARs or the command register.
Exactly, vpci_write needs a write lock, but it is not desirable.
And again, there is a single offending piece of code which wants that...
> Jan
>
Thank you,
Oleksandr