Comment 8 for bug 1805256

I can reproduce this problem with qemu.git/matser. It still exists in qemu.git/matser. I found that when an IO return in worker threads and want to call aio_notify to wake up main_loop, but it found that ctx->notify_me is cleared to 0 by main_loop in aio_ctx_check by calling atomic_and(&ctx->notify_me, ~1) . So worker thread won't write enventfd to notify main_loop.If such a scene happens, the main_loop will hang:
    main loop worker thread1 worker thread2
-----------------------------------------------------------------------------------------------
    qemu_poll_ns aio_worker
                            qemu_bh_schedule(pool->completion_bh)
    glib_pollfds_poll
    g_main_context_check
    aio_ctx_check
    atomic_and(&ctx->notify_me, ~1) aio_worker
                                                      qemu_bh_schedule(pool->completion_bh)
    /* do something for event */
    qemu_poll_ns
    /* hangs !!!*/

As we known, ctx->notify_me will be visited by worker thread and main loop. I thank we should add a lock protection for ctx->notify_me to avoid this happend.what do you thank so?