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Date: Mon, 1 Feb 2016 10:49:00 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3] blockjob: Fix hang in
	block_job_finish_sync
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, Jeff Cody <jcody@redhat.com>, qemu-devel@nongnu.org, mreitz@redhat.com, pbonzini@redhat.com, jsnow@redhat.com

On Fri, 01/29 11:31, Stefan Hajnoczi wrote:
> 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 */

Maybe move one line above in case data->fn() does another
block_job_defer_to_main_loop()?

Fam

> 
>     aio_context_release(aio_context);
> 
>     aio_context_release(data->aio_context);
> 
>     g_free(data);
> }