Am 09.08.2018 um 15:22 hat Fam Zheng geschrieben: > Furthermore, blocking aio_poll is only allowed on home thread > (in_aio_context_home_thread), because otherwise two blocking > aio_poll()'s can steal each other's ctx->notifier event and cause > hanging just like described above.
It's good to have this assertion now at least, but after digging into some bugs, I think in fact that any aio_poll() (even non-blocking) is only allowed in the home thread: At least one reason is that if you run it from a different thread, qemu_get_current_aio_context() returns the wrong AioContext in any callbacks called by aio_poll(). Anything else using TLS can have similar problems. One instance where this matters is fixed/worked around by Sergio's "util/async: use qemu_aio_coroutine_enter in co_schedule_bh_cb". We wouldn't even need that patch if we could make sure that aio_poll() is never called from the wrong thread. This would feel more robust. I'll fix the aio_poll() calls in drain (the AIO_WAIT_WHILE() ones are already fine, the rest by removing them). After that, bdrv_set_aio_context() is still problematic, but the rest should be okay. Hopefully we can use the tighter assertion then. Kevin
