Re: [Qemu-devel] [PATCHv4 01/03] qemu-iothread: IOThread supports the GMainContext event loop

[Fam Zheng <famz@redhat.com>]

On Tue, 08/22 16:46, Wang yong wrote:
> From: Wang Yong <wang.yong155@zte.com.cn>
> 
> IOThread uses AioContext event loop and does not run a GMainContext.
> Therefore,chardev cannot work in IOThread,such as the chardev is
> used for colo-compare packets reception.
> 
> This patch makes the IOThread run the GMainContext event loop,
> chardev and IOThread can work together.
> 
> Signed-off-by: Wang Yong <wang.yong155@zte.com.cn>
> Signed-off-by: Wang Guang <wang.guang55@zte.com.cn>
> ---
>  include/sysemu/iothread.h |  4 ++++
>  iothread.c                | 43 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
> index e6da1a4..d2985b3 100644
> --- a/include/sysemu/iothread.h
> +++ b/include/sysemu/iothread.h
> @@ -24,6 +24,9 @@ typedef struct {
>  
>      QemuThread thread;
>      AioContext *ctx;
> +    GMainContext *worker_context;
> +    GMainLoop *main_loop;
> +    GOnce once;
>      QemuMutex init_done_lock;
>      QemuCond init_done_cond;    /* is thread initialization done? */
>      bool stopping;
> @@ -41,5 +44,6 @@ typedef struct {
>  char *iothread_get_id(IOThread *iothread);
>  AioContext *iothread_get_aio_context(IOThread *iothread);
>  void iothread_stop_all(void);
> +GMainContext *iothread_get_g_main_context(IOThread *iothread);
>  
>  #endif /* IOTHREAD_H */
> diff --git a/iothread.c b/iothread.c
> index beeb870..fb1c55b 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -57,6 +57,20 @@ static void *iothread_run(void *opaque)
>  
>      while (!atomic_read(&iothread->stopping)) {
>          aio_poll(iothread->ctx, true);
> +
> +        if (atomic_read(&iothread->worker_context)) {
> +            g_main_context_push_thread_default(iothread->worker_context);
> +            iothread->main_loop =
> +                g_main_loop_new(iothread->worker_context, TRUE);
> +            g_main_loop_run(iothread->main_loop);
> +
> +            g_main_loop_unref(iothread->main_loop);
> +            iothread->main_loop = NULL;

You should clear iothread->main_loop first before calling g_main_loop_unref(),
to avoid TOCTOU race with iothread_stop():

  iothread_run (in IOThread)          iothread_stop (in main thread)
  ========================================================================
                                      if (atomic_read(&iothread->main_loop)) {
  /* frees iothread->main_loop */
  g_main_loop_unref(...)
                                          /* Accesses freed memory */
                                          g_main_loop_quit(iothread->main_loop)
                                      }
  iothread->main_loop = NULL


> +
> +            g_main_context_pop_thread_default(iothread->worker_context);
> +            g_main_context_unref(iothread->worker_context);
> +            iothread->worker_context = NULL;
> +        }
>      }
>  
>      rcu_unregister_thread();
> @@ -73,6 +87,9 @@ static int iothread_stop(Object *object, void *opaque)
>      }
>      iothread->stopping = true;
>      aio_notify(iothread->ctx);
> +    if (atomic_read(&iothread->main_loop)) {
> +        g_main_loop_quit(iothread->main_loop);
> +    }
>      qemu_thread_join(&iothread->thread);
>      return 0;
>  }
> @@ -125,6 +142,7 @@ static void iothread_complete(UserCreatable *obj, Error **errp)
>  
>      qemu_mutex_init(&iothread->init_done_lock);
>      qemu_cond_init(&iothread->init_done_cond);
> +    iothread->once = (GOnce) G_ONCE_INIT;

Please remove the unnecessary type cast.

>  
>      /* This assumes we are called from a thread with useful CPU affinity for us
>       * to inherit.
> @@ -309,3 +327,28 @@ void iothread_stop_all(void)
>  
>      object_child_foreach(container, iothread_stop, NULL);
>  }
> +
> +static gpointer iothread_g_main_context_init(gpointer opaque)
> +{
> +    AioContext *ctx;
> +    IOThread *iothread = opaque;
> +    GSource *source;
> +
> +    iothread->worker_context = g_main_context_new();
> +
> +    ctx = iothread_get_aio_context(iothread);
> +    source = aio_get_g_source(ctx);
> +    g_source_attach(source, iothread->worker_context);
> +    g_source_unref(source);
> +
> +    aio_notify(iothread->ctx);
> +
> +    return NULL;
> +}
> +
> +GMainContext *iothread_get_g_main_context(IOThread *iothread)
> +{
> +    g_once(&iothread->once, iothread_g_main_context_init, iothread);
> +
> +    return iothread->worker_context;
> +}
> -- 
> 1.8.3.1
> 
> 

Fam