Re: What is bs->reqs_lock for?

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

18.08.2020 09:16, Paolo Bonzini wrote:
> On 13/08/20 18:34, Vladimir Sementsov-Ogievskiy wrote:
>> I thought bs is attached to one aio context and aio context attached to
>> one iothread.
> 
> For now yes, but with multiqueue there would be many iothreads sending
> requests to the AioContext.  The BDS would still have a "home"
> aiocontext to request socket readiness events, but
> io_uring/linux_aio/threadpool requests could be issued from any iothread.
> 
>> And all normal request processing of the bs is done in this one iothread.
>> And when we need to access bs externally, we do it in
>> aio_context_acquire / aio_context_release, which protects from parallel
>> access to BlockDriverState fields...
>>
>> But you say, that block/io.c is not protected by AioContext lock..
>> Does it mean that everything must be thread-safe in block/io.c and all
>> block drivers?
> 
> Yes.
> 
>>
>> Are tracked_requests different from other fields? A lot of other
>> BlockDriverState
>> fields are not protected by any mutex.. For example: total_sectors,
>> file, backing..
> 
> Rules are documented in include/block/block_int.h. 

I should have guessed on my own..

> It seems however
> that never_freeze was blindly added at the end.
> 

Thanks for your answers!


-- 
Best regards,
Vladimir