On Tue, May 05, 2020 at 05:46:18PM +0200, Christoph Hellwig wrote: > On Thu, Apr 30, 2020 at 10:02:54PM +0800, Ming Lei wrote: > > BLK_MQ_S_INACTIVE is only set when the last cpu of this hctx is becoming > > offline, and blk_mq_hctx_notify_offline() is called from cpu hotplug > > handler. So if there is any request of this hctx submitted from somewhere, > > it has to this last cpu. That is done by blk-mq's queue mapping. > > > > In case of direct issue, basically blk_mq_get_driver_tag() is run after > > the request is allocated, that is why I mentioned the chance of > > migration is very small. > > "very small" does not cut it, it has to be zero. And it seems the > new version still has this hack. But smp_mb() is used for ordering the WRITE and READ, so it is correct. barrier() is enough when process migration doesn't happen. thank, Ming
