Messages in this thread | | | Date | Thu, 18 Sep 2014 18:26:38 +0200 | From | Christoph Hellwig <> | Subject | Re: [PATCH 2/2] blk-mq: remove unnecessary blk_clear_rq_complete() |
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On Thu, Sep 18, 2014 at 09:33:35AM +0800, Ming Lei wrote: > > Why yo you think it's not nessecary? The request is not in the drivers > > The COMPLETED flag will be cleared in blk_mq_start_request(), so > it needn't to be cleared here, and it is a bit early and might cause > a tiny race window. > > > hand at this point, so it should not be marked started. Maybe I'm missing > > something, but this sounds like it could very likely cause regressions. > > The STARTED flag has been cleared in __blk_mq_requeue_request(), > I mean the COMPLETED flag, consider the following situation: > > - one req is queued to driver, and the req is completed from > the device just before its timeout expired > - the driver checks the result and finds it need to requeue for some reason > - blk_mq_requeue_request() is called to requeue the req > - COMPLETED is cleared before clearing STARTED because of > writes reorder > - timeout just comes between the two writes > - then the request may be completed another time because of timeout
Ok, I guess you are right on this one. Objection cleared.
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