From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752573Ab2IXJdI (ORCPT ); Mon, 24 Sep 2012 05:33:08 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:36150 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751181Ab2IXJdF (ORCPT ); Mon, 24 Sep 2012 05:33:05 -0400 Message-ID: <1348479181.2467.28.camel@dabdike> Subject: Re: [PATCH scsi] Add NULL checking of return value from scsi_cmd_to_driver() From: James Bottomley To: Li Zhong Cc: LKML , linux-scsi@vger.kernel.org, "Paul E. McKenney" , "Martin K. Petersen" Date: Mon, 24 Sep 2012 13:33:01 +0400 In-Reply-To: <1348478750.2475.51.camel@ThinkPad-T420> References: <1348464626.2475.13.camel@ThinkPad-T420> <1348465493.2467.3.camel@dabdike> <1348470210.2475.47.camel@ThinkPad-T420> <1348472104.2467.8.camel@dabdike> <1348478750.2475.51.camel@ThinkPad-T420> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4 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 On Mon, 2012-09-24 at 17:25 +0800, Li Zhong wrote: > On Mon, 2012-09-24 at 11:35 +0400, James Bottomley wrote: > > On Mon, 2012-09-24 at 15:03 +0800, Li Zhong wrote: > > > On Mon, 2012-09-24 at 09:44 +0400, James Bottomley wrote: > > > > On Mon, 2012-09-24 at 13:30 +0800, Li Zhong wrote: > > > > > Just noticed that after commit 919f797, it is possible that > > > > > scsi_cmd_to_driver() returns NULL. This patch adds the NULL checking for drv > > > > > returned from the above function. > > > > > > > > > > Maybe it is not possible at run time, but from the code itself, we'd better > > > > > have this check? > > > > > > > > There's not much point having a check that never trips, unless it's an > > > > assert, in which case a NULL deref does that. All it does is add > > > > pointless instructions to the critical path. only REQ_TYPE_BLOCK_PC > > > > commands can be submitted without a driver, so the check above would > > > > seem to preclude that. > > > > > > Hi James, > > > > > > Thank you, it sounds reasonable to me. Let's drop it. > > > > Well, there is another thing you might do: The path length of > > scsi_cmd_to_driver() increased a lot thanks to 18a4d0a22ed6 it might be > > worth getting it back to what it was (this looks to be doable with the > > same != REQ_TYPE_BLOCK_PC test in the error handler. Plus, I think it > > fixes a bug where you get different behaviours from REQ_TYPE_BLOCK_PC > > commands when a driver is and isn't attached (I've cc'd Martin to see > > what he thinks). > > Hi James, > > Do you mean something like this: Pretty much, yes. James > ======= > > diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c > index de2337f..c1b05a8 100644 > --- a/drivers/scsi/scsi_error.c > +++ b/drivers/scsi/scsi_error.c > @@ -789,7 +789,6 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd, > int cmnd_size, int timeout, unsigned sense_bytes) > { > struct scsi_device *sdev = scmd->device; > - struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd); > struct Scsi_Host *shost = sdev->host; > DECLARE_COMPLETION_ONSTACK(done); > unsigned long timeleft; > @@ -845,8 +844,11 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd, > > scsi_eh_restore_cmnd(scmd, &ses); > > - if (sdrv && sdrv->eh_action) > - rtn = sdrv->eh_action(scmd, cmnd, cmnd_size, rtn); > + if (scmd->request->cmd_type != REQ_TYPE_BLOCK_PC) { > + struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd); > + if (sdrv->eh_action) > + rtn = sdrv->eh_action(scmd, cmnd, cmnd_size, rtn); > + } > > return rtn; > } > diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h > index ac06cc5..377df4a 100644 > --- a/include/scsi/scsi_cmnd.h > +++ b/include/scsi/scsi_cmnd.h > @@ -134,16 +134,7 @@ struct scsi_cmnd { > > static inline struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd) > { > - struct scsi_driver **sdp; > - > - if (!cmd->request->rq_disk) > - return NULL; > - > - sdp = (struct scsi_driver **)cmd->request->rq_disk->private_data; > - if (!sdp) > - return NULL; > - > - return *sdp; > + return *(struct scsi_driver **)cmd->request->rq_disk->private_data; > } > > extern struct scsi_cmnd *scsi_get_command(struct scsi_device *, gfp_t); > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html