Re: [Qemu-devel] [PATCH] Revert "blockdev: add note that block_job_cb() must be thread-safe"

[Fam Zheng <famz@redhat.com>]

----- Original Message -----
> On Tue, Oct 13, 2015 at 06:16:15PM +0800, Fam Zheng wrote:
> > This reverts commit 723c5d93c51bdb3adbc238ce90195c0864aa6cd5.
> > 
> > block_job_cb is called by block_job_completed, which is always called in
> > a main loop bottom half in existing block jobs. So we don't need to
> > worry about thread-safety here.
> 
> This is not correct.  Search for block_job_completed() callers.
> 
> For example, block/stream.c has early exit cases that call
> block_job_completed() from the coroutine (i.e. dispatched from a
> coroutine in another AioContext+IOThread).
> 
> I think you are assuming that all block_job_completed() callers are
> called from a function scheduled using block_job_defer_to_main_loop().

No, I'm assuming all block_job_completed() callers are (and they should
be) from main thread. Even the early exit cases in stream are so, because
they are in the same thread as stream_start, which is main thread.

> 
> Please double-check this.
> 
> Thanks,
> Stefan
> 
>