From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751624AbdLLL5J (ORCPT ); Tue, 12 Dec 2017 06:57:09 -0500 Received: from merlin.infradead.org ([205.233.59.134]:59208 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750731AbdLLL5I (ORCPT ); Tue, 12 Dec 2017 06:57:08 -0500 Date: Tue, 12 Dec 2017 12:56:57 +0100 From: Peter Zijlstra To: Tejun Heo Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, oleg@redhat.com, kernel-team@fb.com, osandov@fb.com Subject: Re: [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme Message-ID: <20171212115657.t6z4l3wilvnzs4ue@hirez.programming.kicks-ass.net> References: <20171209192525.982030-1-tj@kernel.org> <20171209192525.982030-3-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171209192525.982030-3-tj@kernel.org> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Dec 09, 2017 at 11:25:21AM -0800, Tejun Heo wrote: > +static inline void blk_mq_rq_update_state(struct request *rq, > + enum mq_rq_state state) > +{ > + u64 new_val = (rq->gstate & ~MQ_RQ_STATE_MASK) | state; > + > + if (state == MQ_RQ_IN_FLIGHT) { > + WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE); > + new_val += MQ_RQ_GEN_INC; > + } > + > + /* avoid exposing interim values */ My paranoia would like to see READ_ONCE() on the rq->gstate load above as well, that makes it a fully explicit load-store operation. > + WRITE_ONCE(rq->gstate, new_val); > +}