On 03/23/2017 01:39 PM, Paolo Bonzini wrote:
> All block jobs are using block_job_defer_to_main_loop as the final
> step just before the coroutine terminates. At this point,
> block_job_enter should do nothing, but currently it restarts
> the freed coroutine.
>
> Now, the job->co states should probably be changed to an enum
> (e.g. BEFORE_START, STARTED, YIELDED, COMPLETED) subsuming
Yes, I'd love to formalize the FSM for jobs.
> block_job_started, job->deferred_to_main_loop and job->busy.
> For now, this patch eliminates the problematic reenter by
> removing the reset of job->deferred_to_main_loop (which served
> no purpose, as far as I could see) and checking the flag in
> block_job_enter.
Not sure -- the original commit 794f01414 makes it seem like it should
stay so that the correct AIO context can be acquired. Probably a race as
jobs don't often stay long once they've deferred to the main loop, but I
think the reset is harmless as you say.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> blockjob.c | 10 ++++++++--
> include/block/blockjob_int.h | 3 ++-
> 2 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/blockjob.c b/blockjob.c
> index 3fa2885..2d80dae 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -750,7 +750,14 @@ void block_job_resume_all(void)
>
> void block_job_enter(BlockJob *job)
> {
> - if (job->co && !job->busy) {
> + if (!block_job_started(job)) {
> + return;
> + }
> + if (job->deferred_to_main_loop) {
> + return;
> + }
> +
> + if (!job->busy) {
> qemu_coroutine_enter(job->co);
> }
> }
> @@ -874,7 +881,6 @@ static void block_job_defer_to_main_loop_bh(void *opaque)
> aio_context_acquire(aio_context);
> }
>
> - data->job->deferred_to_main_loop = false;
> data->fn(data->job, data->opaque);
>
> if (aio_context != data->aio_context) {
> diff --git a/include/block/blockjob_int.h b/include/block/blockjob_int.h
> index 97ffc43..4d287ba 100644
> --- a/include/block/blockjob_int.h
> +++ b/include/block/blockjob_int.h
> @@ -227,7 +227,8 @@ typedef void BlockJobDeferToMainLoopFn(BlockJob *job,
> void *opaque);
> * @fn: The function to run in the main loop
> * @opaque: The opaque value that is passed to @fn
> *
> - * Execute a given function in the main loop with the BlockDriverState
> + * This function must be called by the main job coroutine just before it
> + * returns. @fn is executed in the main loop with the BlockDriverState
> * AioContext acquired. Block jobs must call bdrv_unref(), bdrv_close(), and
> * anything that uses bdrv_drain_all() in the main loop.
> *
>
Reviewed-by: John Snow <js...@redhat.com>
