From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [PATCH scsi] Add NULL checking of return value from scsi_cmd_to_driver() Date: Mon, 24 Sep 2012 11:35:04 +0400 Message-ID: <1348472104.2467.8.camel@dabdike> References: <1348464626.2475.13.camel@ThinkPad-T420> <1348465493.2467.3.camel@dabdike> <1348470210.2475.47.camel@ThinkPad-T420> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1348470210.2475.47.camel@ThinkPad-T420> Sender: linux-kernel-owner@vger.kernel.org To: Li Zhong Cc: LKML , linux-scsi@vger.kernel.org, "Paul E. McKenney" , "Martin K. Petersen" List-Id: linux-scsi@vger.kernel.org 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). James