On Fri, 09/07 17:51, Kevin Wolf wrote: > 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.
Fully agree with you. Fam