Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932369AbcCPPrl (ORCPT ); Wed, 16 Mar 2016 11:47:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33936 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751485AbcCPPr3 (ORCPT ); Wed, 16 Mar 2016 11:47:29 -0400 Subject: Re: [PATCH] qla2xxx: avoid maybe_uninitialized warning From: "Ewan D. Milne" Reply-To: emilne@redhat.com To: Tomas Henzl Cc: Arnd Bergmann , qla2xxx-upstream@qlogic.com, "James E.J. Bottomley" , "Martin K. Petersen" , Nicholas Bellinger , Himanshu Madhani , Quinn Tran , Alexei Potashnik , Bart Van Assche , Swapnil Nagle , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <56E975B8.6040807@redhat.com> References: <1458078051-529344-1-git-send-email-arnd@arndb.de> <56E975B8.6040807@redhat.com> Content-Type: text/plain; charset="UTF-8" Organization: Red Hat Date: Wed, 16 Mar 2016 11:47:26 -0400 Message-ID: <1458143246.17965.10.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3595 Lines: 77 On Wed, 2016-03-16 at 16:03 +0100, Tomas Henzl wrote: > On 15.3.2016 22:40, Arnd Bergmann wrote: > > The qlt_check_reserve_free_req() function produces an incorrect warning > > when CONFIG_PROFILE_ANNOTATED_BRANCHES is set: > > > > drivers/scsi/qla2xxx/qla_target.c: In function 'qlt_check_reserve_free_req': > > drivers/scsi/qla2xxx/qla_target.c:1887:3: error: 'cnt_in' may be used uninitialized in this function [-Werror=maybe-uninitialized] > > ql_dbg(ql_dbg_io, vha, 0x305a, > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > "qla_target(%d): There is no room in the request ring: vha->req->ring_index=%d, vha->req->cnt=%d, req_cnt=%d Req-out=%d Req-in=%d Req-Length=%d\n", > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > vha->vp_idx, vha->req->ring_index, > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > vha->req->cnt, req_cnt, cnt, cnt_in, vha->req->length); > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > drivers/scsi/qla2xxx/qla_target.c:1887:3: error: 'cnt' may be used uninitialized in this function [-Werror=maybe-uninitialized] > > > > The problem is that gcc fails to track the state of the condition across > > an annotated branch. > > > > This slightly rearranges the code to move the second if() block > > into the first one, to avoid the warning while retaining the > > behavior of the code. > > When the first 'if' is true the vha->req->ring_index gets a new value > assigned - so it could be possible that the second 'if' wont be true any more. > The code should not be merged into that single 'if', or am I missing something? > > tomash If the first "if" is false, the second "if" will be false also, because the vha->req->cnt value has not changed. If the first "if" is true, the nested second "if" will retest the condition. The compiler is not at fault, because vha->req->cnt can't be tracked as it could be modified by another thread/process. It isn't, it's protected by the ->hardware_lock, but the compiler doesn't know that. -Ewan > > > > Signed-off-by: Arnd Bergmann > > --- > > drivers/scsi/qla2xxx/qla_target.c | 16 +++++++++------- > > 1 file changed, 9 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/scsi/qla2xxx/qla_target.c b/drivers/scsi/qla2xxx/qla_target.c > > index 985231900aca..8a44d1541eb4 100644 > > --- a/drivers/scsi/qla2xxx/qla_target.c > > +++ b/drivers/scsi/qla2xxx/qla_target.c > > @@ -1881,15 +1881,17 @@ static int qlt_check_reserve_free_req(struct scsi_qla_host *vha, > > else > > vha->req->cnt = vha->req->length - > > (vha->req->ring_index - cnt); > > - } > > > > - if (unlikely(vha->req->cnt < (req_cnt + 2))) { > > - ql_dbg(ql_dbg_io, vha, 0x305a, > > - "qla_target(%d): There is no room in the request ring: vha->req->ring_index=%d, vha->req->cnt=%d, req_cnt=%d Req-out=%d Req-in=%d Req-Length=%d\n", > > - vha->vp_idx, vha->req->ring_index, > > - vha->req->cnt, req_cnt, cnt, cnt_in, vha->req->length); > > - return -EAGAIN; > > + if (unlikely(vha->req->cnt < (req_cnt + 2))) { > > + ql_dbg(ql_dbg_io, vha, 0x305a, > > + "qla_target(%d): There is no room in the request ring: vha->req->ring_index=%d, vha->req->cnt=%d, req_cnt=%d Req-out=%d Req-in=%d Req-Length=%d\n", > > + vha->vp_idx, vha->req->ring_index, > > + vha->req->cnt, req_cnt, cnt, cnt_in, > > + vha->req->length); > > + return -EAGAIN; > > + } > > } > > + > > vha->req->cnt -= req_cnt; > > > > return 0; >