Re: [RFC PATCH 0/5] Removal of AioContext lock, bs->parents and ->children: proof of concept

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

Am 09/03/2022 um 14:26 schrieb Emanuele Giuseppe Esposito:
>> Next, I have a problem in mind, that in past lead to a lot of iotest 30
>> failures. Next there were different fixes and improvements, but the core
>> problem (as far as I understand) is still here: nothing protects us when
>> we are in some graph modification process (for example block-job
>> finalization) do yield, switch to other coroutine and enter another
>> graph modification process (for example, another block-job finaliztion)..
> That's another point to consider. I don't really have a solution for this.
> 
On a side note, that might not be a real problem.
If I understand correctly, your fear is that we are doing something like
parent->children[x] = new_node // partial graph operation
/* yield to another coroutine */
coroutine reads/writes parent->children[x] and/or new_node->parents[y]
/* yield back */
new_node->parents[y] = parent // end of the initial graph operation

Is that what you are pointing out here?
If so, is there a concrete example for this? Because yields and drains
(that eventually can poll) seem to be put either before or after the
whole graph modification section. In other words, even if a coroutine
enters, it will be always before or after the _whole_ graph modification
is performed.

Thank you,
Emanuele