Re: [PATCH v3 01/16] job.c: make job_mutex and job_lock/unlock() public

[Paolo Bonzini <pbonzini@redhat.com>]

On 1/5/22 15:01, Emanuele Giuseppe Esposito wrote:
> job mutex will be used to protect the job struct elements and list,
> replacing AioContext locks.
> 
> Right now use a shared lock for all jobs, in order to keep things
> simple. Once the AioContext lock is gone, we can introduce per-job
> locks.

Not even needed in my opinion, this is not a fast path.  But we'll see.

> To simplify the switch from aiocontext to job lock, introduce
> *nop* lock/unlock functions and macros. Once everything is protected
> by jobs, we can add the mutex and remove the aiocontext.
> 
> Since job_mutex is already being used, add static
> real_job_{lock/unlock}.

Out of curiosity, what breaks if the real job lock is used from the 
start?  (It probably should be mentioned in the commit message).


> -static void job_lock(void)
> +static void real_job_lock(void)
>   {
>       qemu_mutex_lock(&job_mutex);
>   }
>   
> -static void job_unlock(void)
> +static void real_job_unlock(void)
>   {
>       qemu_mutex_unlock(&job_mutex);
>   }

Would it work to

#define job_lock real_job_lock
#define job_unlock real_job_unlock

instead of having to do the changes below?

Paolo

> @@ -449,21 +460,21 @@ void job_enter_cond(Job *job, bool(*fn)(Job *job))
>           return;
>       }
>   
> -    job_lock();
> +    real_job_lock();
>       if (job->busy) {
> -        job_unlock();
> +        real_job_unlock();
>           return;
>       }
>   
>       if (fn && !fn(job)) {
> -        job_unlock();
> +        real_job_unlock();
>           return;
>       }
>   
>       assert(!job->deferred_to_main_loop);
>       timer_del(&job->sleep_timer);
>       job->busy = true;
> -    job_unlock();
> +    real_job_unlock();
>       aio_co_enter(job->aio_context, job->co);
>   }
>   
> @@ -480,13 +491,13 @@ void job_enter(Job *job)
>    * called explicitly. */
>   static void coroutine_fn job_do_yield(Job *job, uint64_t ns)
>   {
> -    job_lock();
> +    real_job_lock();
>       if (ns != -1) {
>           timer_mod(&job->sleep_timer, ns);
>       }
>       job->busy = false;
>       job_event_idle(job);
> -    job_unlock();
> +    real_job_unlock();
>       qemu_coroutine_yield();
>   
>       /* Set by job_enter_cond() before re-entering the coroutine.  */