Re: [RFC PATCH 0/6] job: replace AioContext lock with job_mutex

[Stefan Hajnoczi]

On Wed, Jul 07, 2021 at 06:58:07PM +0200, Emanuele Giuseppe Esposito wrote:
> This is a continuation on the work to reduce (and possibly get rid of) the 
> usage of AioContext lock, by introducing smaller granularity locks to keep 
> the thread safety.
> 
> This series aims to:
> 1) remove the aiocontext lock and substitute it with the already existing
>    global job_mutex
> 2) fix what it looks like to be an oversight when moving the blockjob.c logic
>    into the more generic job.c: job_mutex was introduced especially to
>    protect job->busy flag, but it seems that it was not used in successive
>    patches, because there are multiple code sections that directly
>    access the field without any locking.
> 3) use job_mutex instead of the aiocontext_lock
> 4) extend the reach of the job_mutex to protect all shared fields
>    that the job structure has.

Can you explain the big picture:

1. What are the rules for JobDrivers? Imagine you are implementing a new
   JobDriver. What do you need to know in order to write correct code?

2. What are the rules for monitor? The main pattern is looking up a job,
   invoking a job API on it, and then calling job_unlock().

Stefan

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