Re: What is bs->reqs_lock for?

[Vladimir Sementsov-Ogievskiy]

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