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Re: What is bs->reqs_lock for?

From: Vladimir Sementsov-Ogievskiy
Subject: Re: What is bs->reqs_lock for?
Date: Wed, 19 Aug 2020 12:41:28 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0

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?


Are tracked_requests different from other fields? A lot of other
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,

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