From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from esa2.hgst.iphmx.com ([68.232.143.124]:17442 "EHLO esa2.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751677AbdFFQEF (ORCPT ); Tue, 6 Jun 2017 12:04:05 -0400 From: Bart Van Assche To: "hch@infradead.org" , "linux-block@vger.kernel.org" , "axboe@fb.com" , "ming.lei@redhat.com" Subject: Re: [PATCH v5 08/12] blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue Date: Tue, 6 Jun 2017 16:03:48 +0000 Message-ID: <1496765026.2692.8.camel@sandisk.com> References: <20170606152210.22806-1-ming.lei@redhat.com> <20170606152210.22806-9-ming.lei@redhat.com> In-Reply-To: <20170606152210.22806-9-ming.lei@redhat.com> Content-Type: text/plain; charset="iso-8859-1" MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Tue, 2017-06-06 at 23:22 +0800, Ming Lei wrote: > It is required that no dispatch can happen any more once > blk_mq_quiesce_queue() returns, and we don't have such requirement > on APIs of stopping queue. >=20 > But blk_mq_quiesce_queue() still may not block/drain dispatch in the > the case of BLK_MQ_S_START_ON_RUN, so use the new introduced flag of > QUEUE_FLAG_QUIESCED and evaluate it inside RCU read-side critical > sections for fixing this issue. >=20 > Also blk_mq_quiesce_queue() is implemented via stopping queue, which > limits its uses, and easy to cause race, because any queue restart in > other paths may break blk_mq_quiesce_queue(). With the introduced > flag of QUEUE_FLAG_QUIESCED, we don't need to depend on stopping queue > for quiescing any more. Reviewed-by: Bart Van Assche =