On 23/02/2016 06:57, Fam Zheng wrote: >>>> + qed_cancel_need_check_timer(s); >>>> + qed_need_check_timer_cb(s); >>>> + } >>> >>> What if an allocating write is queued (the else branch case)? Its completion >>> will be in bdrv_drain and it could arm the need_check_timer which is wrong. >>> >>> We need to drain the allocating_write_reqs queue before checking the timer. >> >> You're right, but how? That's what bdrv_drain(bs) does, it's a >> chicken-and-egg problem. > > Maybe use an aio_poll loop before the if?
That would not change the fact that you're reimplementing bdrv_drain inside bdrv_qed_drain. Perhaps for now it's simplest to just remove the QED .bdrv_drain callback, if you think this patch is not a good stopgap measure to avoid the segmentation faults. Once the bdrv_drain rework is in, we can move the callback _after_ I/O is drained on bs and before it is drained on bs->file->bs. Paolo