Hi ming On 04/29/2018 09:36 AM, Ming Lei wrote: > On Sun, Apr 29, 2018 at 6:27 AM, Ming Lei <tom.leiming@xxxxxxxxx> wrote: >> On Sun, Apr 29, 2018 at 5:57 AM, Ming Lei <tom.leiming@xxxxxxxxx> wrote: >>> On Sat, Apr 28, 2018 at 10:00 PM, jianchao.wang >>> <jianchao.w.wang@xxxxxxxxxx> wrote: >>>> Hi ming >>>> >>>> On 04/27/2018 10:57 PM, Ming Lei wrote: >>>>> I may not understand your point, once blk_sync_queue() returns, the >>>>> timer itself is deactivated, meantime the synced .nvme_timeout() only >>>>> returns EH_NOT_HANDLED before the deactivation. >>>>> >>>>> That means this timer won't be expired any more, so could you explain >>>>> a bit why timeout can come again after blk_sync_queue() returns >>>> >>>> Please consider the following case: >>>> >>>> blk_sync_queue >>>> -> del_timer_sync >>>> blk_mq_timeout_work >>>> -> blk_mq_check_expired // return the timeout value >>>> -> blk_mq_terninate_expired >>>> -> .timeout //return EH_NOT_HANDLED >>>> -> mod_timer // setup the timer again based on the result of blk_mq_check_expired >>>> -> cancel_work_sync >>>> So after the blk_sync_queue, the timer may come back again, then the timeout work. >>> >>> OK, I was trying to avoid to use blk_abort_request(), but looks we >>> may have to depend on it or similar way. >>> >>> BTW, that means blk_sync_queue() has been broken, even though the uses >>> in blk_cleanup_queue(). >>> >>> Another approach is to introduce one perpcu_ref of >>> 'q->timeout_usage_counter' for >>> syncing timeout, seems a bit over-kill too, but simpler in both theory >>> and implement. >> >> Or one timout_mutex is enough. > > Turns out it is SRCU. > after split the timeout path into timer and workqueue two parts, if we don't drain the in-flight requests, the request_queue->timeout and the timeout work look like an issue of 'chicken and egg'. how about introduce a flag to disable triggering of timeout work ? Thanks Jianchao
