Re: [Qemu-devel] [PATCH v3] blockjob: Fix hang in block_job_finish_sync

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Fri, Jan 29, 2016 at 10:19:49AM +0800, Fam Zheng wrote:
> @@ -402,6 +407,10 @@ typedef void BlockJobDeferToMainLoopFn(BlockJob *job, void *opaque);
>   * AioContext acquired.  Block jobs must call bdrv_unref(), bdrv_close(), and
>   * anything that uses bdrv_drain_all() in the main loop.
>   *
> + * The job->deferred_to_main_loop flag will be set. Caller must clear it once
> + * the deferred work is done and the block job coroutine continues, unless it's
> + * completing immediately.
> + *

It's not necessary to expose job->deferred_to_main_loop to the user.
Just clear it:

static void block_job_defer_to_main_loop_bh(void *opaque)
{
    BlockJobDeferToMainLoopData *data = opaque;
    AioContext *aio_context;

    qemu_bh_delete(data->bh);

    /* Prevent race with block_job_defer_to_main_loop() */
    aio_context_acquire(data->aio_context);

    /* Fetch BDS AioContext again, in case it has changed */
    aio_context = bdrv_get_aio_context(data->job->bs);
    aio_context_acquire(aio_context);

    data->fn(data->job, data->opaque);
    job->deferred_to_main_loop = false;  /* <----- HERE */

    aio_context_release(aio_context);

    aio_context_release(data->aio_context);

    g_free(data);
}

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