From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69652C43381 for ; Tue, 2 Apr 2019 02:10:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FC3A20833 for ; Tue, 2 Apr 2019 02:10:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726411AbfDBCKu (ORCPT ); Mon, 1 Apr 2019 22:10:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17670 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726269AbfDBCKu (ORCPT ); Mon, 1 Apr 2019 22:10:50 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0FDEC307B95F; Tue, 2 Apr 2019 02:10:50 +0000 (UTC) Received: from ming.t460p (ovpn-8-17.pek2.redhat.com [10.72.8.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C82C16B8E4; Tue, 2 Apr 2019 02:10:45 +0000 (UTC) Date: Tue, 2 Apr 2019 10:10:40 +0800 From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org Subject: Re: [PATCH] block: fix build warning in __blk_bios_map_sg() Message-ID: <20190402021039.GA26316@ming.t460p> References: <20190402014638.25633-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190402014638.25633-1-ming.lei@redhat.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Tue, 02 Apr 2019 02:10:50 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Apr 02, 2019 at 09:46:38AM +0800, Ming Lei wrote: > Commit f6970f83ef79 ("block: don't check if adjacent bvecs in one bio can > be mergeable") changes bvec merge by only considering two bvecs from > different bios. However, if the former bio doesn't inlcude any io bvec, > then the following warning may be triggered: > > warning: ‘bvec.bv_offset’ may be used uninitialized in this function [-Wmaybe-uninitialized] > > In practice, it shouldn't be triggered. > > Fixes it by adding check on former bio, the check shouldn't add any cost > given 'bio->bi_iter' can be hit in cache. > > Reported-by: Jens Axboe > Fixes: f6970f83ef79 ("block: don't check if adjacent bvecs in one bio can be mergeable") > Signed-off-by: Ming Lei > --- > block/blk-merge.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index 8f96d683b577..1fc66d03893f 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -527,7 +527,7 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio, > struct scatterlist *sglist, > struct scatterlist **sg) > { > - struct bio_vec bvec, bvprv = { NULL }; > + struct bio_vec uninitialized_var(bvec), bvprv = { NULL }; > struct bvec_iter iter; > int nsegs = 0; > bool new_bio = false; > @@ -550,8 +550,10 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio, > next_bvec: > new_bio = false; > } > - bvprv = bvec; > - new_bio = true; > + if (likely(bio->bi_iter.bi_size)) { > + bvprv = bvec; > + new_bio = true; > + } > } Looks __blk_recalc_rq_segments() needs the similar fix too, so please ignore this one, and I will handle them all in one patch. Thanks, Ming