On Wed, Aug 29, 2018 at 09:57:28PM -0400, John Snow wrote: > All jobs do the same thing when they leave their running loop: > - Store the return code in a structure > - wait to receive this structure in the main thread > - signal job completion via job_completed > > Few jobs do anything beyond exactly this. Consolidate this exit > logic for a net reduction in SLOC. > > More seriously, when we utilize job_defer_to_main_loop_bh to call > a function that calls job_completed, job_finalize_single will run > in a context where it has recursively taken the aio_context lock, > which can cause hangs if it puts down a reference that causes a flush. > > You can observe this in practice by looking at mirror_exit's careful > placement of job_completed and bdrv_unref calls. > > If we centralize job exiting, we can signal job completion from outside > of the aio_context, which should allow for job cleanup code to run with > only one lock, which makes cleanup callbacks less tricky to write. > > Signed-off-by: John Snow <js...@redhat.com> > Reviewed-by: Max Reitz <mre...@redhat.com>
Reviewed-by: Jeff Cody <jc...@redhat.com> > --- > include/qemu/job.h | 11 +++++++++++ > job.c | 18 ++++++++++++++++++ > 2 files changed, 29 insertions(+) > > diff --git a/include/qemu/job.h b/include/qemu/job.h > index e0e99870a1..1144d671a1 100644 > --- a/include/qemu/job.h > +++ b/include/qemu/job.h > @@ -208,6 +208,17 @@ struct JobDriver { > */ > void (*drain)(Job *job); > > + /** > + * If the callback is not NULL, exit will be invoked from the main thread > + * when the job's coroutine has finished, but before transactional > + * convergence; before @prepare or @abort. > + * > + * FIXME TODO: This callback is only temporary to transition remaining > jobs > + * to prepare/commit/abort/clean callbacks and will be removed before > 3.1. > + * is released. > + */ > + void (*exit)(Job *job); > + > /** > * If the callback is not NULL, prepare will be invoked when all the jobs > * belonging to the same transaction complete; or upon this job's > completion > diff --git a/job.c b/job.c > index bc1d970df4..bc8dad4e71 100644 > --- a/job.c > +++ b/job.c > @@ -535,6 +535,18 @@ void job_drain(Job *job) > } > } > > +static void job_exit(void *opaque) > +{ > + Job *job = (Job *)opaque; > + AioContext *aio_context = job->aio_context; > + > + if (job->driver->exit) { > + aio_context_acquire(aio_context); > + job->driver->exit(job); > + aio_context_release(aio_context); > + } > + job_completed(job, job->ret); > +} > > /** > * All jobs must allow a pause point before entering their job proper. This > @@ -547,6 +559,12 @@ static void coroutine_fn job_co_entry(void *opaque) > assert(job && job->driver && job->driver->run); > job_pause_point(job); > job->ret = job->driver->run(job, &job->err); > + if (!job->deferred_to_main_loop) { > + job->deferred_to_main_loop = true; > + aio_bh_schedule_oneshot(qemu_get_aio_context(), > + job_exit, > + job); > + } > } > > > -- > 2.14.4 >