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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan