Re: [Qemu-devel] A glib warning encountered with internal iothread

[Stefan Hajnoczi]

On Tue, Sep 26, 2017 at 07:13:43PM +0800, Fam Zheng wrote:
> On Tue, 09/26 17:11, Peter Xu wrote:
>  void aio_context_unref(AioContext *ctx)
>  {
> +    assert(ctx->refcnt > 0);
> +    if (--ctx->refcnt == 0) {
> +        aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL);
> +    }

This isn't a general solution because Linux AIO also has a file
descriptor that is removed in aio_ctx_finalize().

Here is a different approach.  Does it work for you?

BTW I'm not a glib expert so maybe we're abusing the API and missing the
obvious way to structure our code :).

diff --git a/util/aio-posix.c b/util/aio-posix.c
index 2d51239ec6..5946ac09f0 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -223,7 +223,14 @@ void aio_set_fd_handler(AioContext *ctx,
             return;
         }

-        g_source_remove_poll(&ctx->source, &node->pfd);
+        /* If the GSource is in the process of being destroyed then
+         * g_source_remove_poll() causes an assertion failure.  Skip
+         * removal in that case, because glib cleans up its state during
+         * destruction anyway.
+         */
+        if (!g_source_is_destroyed(&ctx->source)) {
+            g_source_remove_poll(&ctx->source, &node->pfd);
+        }

         /* If the lock is held, just mark the node as deleted */
         if (qemu_lockcnt_count(&ctx->list_lock)) {