From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steffen Maier Subject: Re: [PATCH v2 02/16] scsi: don't use fc_bsg_job::request and fc_bsg_job::reply directly Date: Fri, 28 Oct 2016 11:53:46 +0200 Message-ID: <4b411836-e76f-b67a-3d49-ad3d51b8f216@linux.vnet.ibm.com> References: <2ea07f3f-88eb-b795-fa37-a223bf80e581@linux.vnet.ibm.com> <20161013162405.aoxy3bdkc4bqtwsk@linux-x5ow.site> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8BIT Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:34551 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753390AbcJ1JyA (ORCPT ); Fri, 28 Oct 2016 05:54:00 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u9S9rxP9085414 for ; Fri, 28 Oct 2016 05:53:59 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0b-001b2d01.pphosted.com with ESMTP id 26c2qe4gsw-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 28 Oct 2016 05:53:59 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 28 Oct 2016 10:53:54 +0100 In-Reply-To: <20161013162405.aoxy3bdkc4bqtwsk@linux-x5ow.site> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Johannes Thumshirn Cc: "Martin K . Petersen" , Christoph Hellwig , Hannes Reinecke , Linux Kernel Mailinglist , Linux SCSI Mailinglist , Martin Schwidefsky , Heiko Carstens , Anil Gurumurthy , Sudarsana Kalluru , "James E.J. Bottomley" , Tyrel Datwyler , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Johannes Thumshirn , James Smart , Dick Kennedy s On 10/13/2016 06:24 PM, Johannes Thumshirn wrote: > On Thu, Oct 13, 2016 at 05:15:25PM +0200, Steffen Maier wrote: >> I'm puzzled. >> >> $ git bisect start fc_bsg master >>> 3087864ce3d7282f59021245d8a5f83ef1caef18 is the first bad commit >>> commit 3087864ce3d7282f59021245d8a5f83ef1caef18 >>> Author: Johannes Thumshirn >>> Date: Wed Oct 12 15:06:28 2016 +0200 >>> >>> scsi: don't use fc_bsg_job::request and fc_bsg_job::reply directly >>> >>> Don't use fc_bsg_job::request and fc_bsg_job::reply directly, but use >>> helper variables bsg_request and bsg_reply. This will be helpfull when >>> transitioning to bsg-lib. >>> >>> Signed-off-by: Johannes Thumshirn >>> >>> :040000 040000 140c4b6829d5cfaec4079716e0795f63f8bc3bd2 0d9fe225615679550be91fbd9f84c09ab1e280fc M drivers >> >> From there (on the reverse bisect path) I get the following Oops, >> except for the full patch set having another stack trace as in my previous >> mail (dying in zfcp code). >> > > [...] > >> >>> @@ -3937,6 +3944,7 @@ fc_bsg_request_handler(struct request_queue *q, struct Scsi_Host *shost, >>> struct request *req; >>> struct fc_bsg_job *job; >>> enum fc_dispatch_result ret; >>> + struct fc_bsg_reply *bsg_reply; >>> >>> if (!get_device(dev)) >>> return; >>> @@ -3973,8 +3981,9 @@ fc_bsg_request_handler(struct request_queue *q, struct Scsi_Host *shost, >>> /* check if we have the msgcode value at least */ >>> if (job->request_len < sizeof(uint32_t)) { >>> BUG_ON(job->reply_len < sizeof(uint32_t)); >>> - job->reply->reply_payload_rcv_len = 0; >>> - job->reply->result = -ENOMSG; >>> + bsg_reply = job->reply; >>> + bsg_reply->reply_payload_rcv_len = 0; >>> + bsg_reply->result = -ENOMSG; Compiler optimization re-ordered above two lines and the first pointer derefence is bsg_reply->result [field offset 0] where bsg_reply is NULL. The assignment tries to write to memory at address NULL causing the kernel page fault. Does your suggested change for [PATCH v3 02/16], shuffling the job->request_len checks, address above kernel page fault? >>> job->reply_len = sizeof(uint32_t); >>> fc_bsg_jobdone(job); >>> spin_lock_irq(q->queue_lock); >>> > > Ahm and what exactly can break here? It's just assigning variables. Now > I'm puzzled too. -- Mit freundlichen Grüßen / Kind regards Steffen Maier Linux on z Systems Development IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz Geschaeftsfuehrung: Dirk Wittkopp Sitz der Gesellschaft: Boeblingen Registergericht: Amtsgericht Stuttgart, HRB 243294