From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:56894 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732326AbeIXS0t (ORCPT ); Mon, 24 Sep 2018 14:26:49 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andrew Jones , Omar Sandoval , Bart Van Assche , linux-scsi@vger.kernel.org, "Martin K. Petersen" , Christoph Hellwig , Ming Lei , Jens Axboe , Sasha Levin Subject: [PATCH 4.14 155/173] blk-mq: avoid to synchronize rcu inside blk_cleanup_queue() Date: Mon, 24 Sep 2018 13:53:09 +0200 Message-Id: <20180924113126.670088676@linuxfoundation.org> In-Reply-To: <20180924113114.334025954@linuxfoundation.org> References: <20180924113114.334025954@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ming Lei [ Upstream commit 1311326cf4755c7ffefd20f576144ecf46d9906b ] SCSI probing may synchronously create and destroy a lot of request_queues for non-existent devices. Any synchronize_rcu() in queue creation or destroy path may introduce long latency during booting, see detailed description in comment of blk_register_queue(). This patch removes one synchronize_rcu() inside blk_cleanup_queue() for this case, commit c2856ae2f315d75(blk-mq: quiesce queue before freeing queue) needs synchronize_rcu() for implementing blk_mq_quiesce_queue(), but when queue isn't initialized, it isn't necessary to do that since only pass-through requests are involved, no original issue in scsi_execute() at all. Without this patch and previous one, it may take more 20+ seconds for virtio-scsi to complete disk probe. With the two patches, the time becomes less than 100ms. Fixes: c2856ae2f315d75 ("blk-mq: quiesce queue before freeing queue") Reported-by: Andrew Jones Cc: Omar Sandoval Cc: Bart Van Assche Cc: linux-scsi@vger.kernel.org Cc: "Martin K. Petersen" Cc: Christoph Hellwig Tested-by: Andrew Jones Signed-off-by: Ming Lei Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- block/blk-core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/block/blk-core.c +++ b/block/blk-core.c @@ -669,9 +669,13 @@ void blk_cleanup_queue(struct request_qu * make sure all in-progress dispatch are completed because * blk_freeze_queue() can only complete all requests, and * dispatch may still be in-progress since we dispatch requests - * from more than one contexts + * from more than one contexts. + * + * No need to quiesce queue if it isn't initialized yet since + * blk_freeze_queue() should be enough for cases of passthrough + * request. */ - if (q->mq_ops) + if (q->mq_ops && blk_queue_init_done(q)) blk_mq_quiesce_queue(q); /* for synchronous bio-based driver finish in-flight integrity i/o */