From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756055Ab0IQSZs (ORCPT ); Fri, 17 Sep 2010 14:25:48 -0400 Received: from smtp102.sbc.mail.ne1.yahoo.com ([98.138.84.213]:48171 "HELO smtp102.sbc.mail.ne1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754938Ab0IQSZp (ORCPT ); Fri, 17 Sep 2010 14:25:45 -0400 X-Yahoo-SMTP: fzDSGlOswBCWnIOrNw7KwwK1j9PqyNbe5PtLKiS4dDU.UNl_t6bdEZu9tTLW X-YMail-OSG: F7YJSI4VM1kSABdCDhO5ZmKQvlV2mKVOz1MlTADrtMdThPi gnvcU0gIP6SPzAy1FPd4zSV1MfEK421UWJzqPoDPwgJjvkxg5qPnd65Fl9yv TFlBUQJGvvx4e1PAaTn2o6_BsE2lmIu130oKV1x8irw.cp5j_tO_xhxim.Xv 9nn8AeODn3EtUyCJInN8fgy30kf5Kkzv0ngAoALx1tp7846Ozj91RjUCLP8G UoK9P4bRa04LcSnvbF9jj03AtY4oCLr_8fkjhmiyNhsbbs5UBd1CeypjDpmS OedpA0d31qo1YWU3Sx7j57DQ- X-Yahoo-Newman-Property: ymail-3 Subject: Re: [PATCH 1/8] scsi: Drop struct Scsi_Host->host_lock around SHT->queuecommand() From: "Nicholas A. Bellinger" To: Tim Chen Cc: James Bottomley , Andi Kleen , linux-scsi , linux-kernel , Vasu Dev , Matthew Wilcox , Mike Christie , James Smart , Andrew Vasquez , FUJITA Tomonori , Hannes Reinecke , Joe Eykholt , Christoph Hellwig In-Reply-To: <1284745799.7280.155.camel@schen9-DESK> References: <1284676529-10756-1-git-send-email-nab@linux-iscsi.org> <1284691571.26423.50.camel@mulgrave.site> <20100917072022.GB2644@gargoyle.ger.corp.intel.com> <1284725592.26423.60.camel@mulgrave.site> <4C9379AA.4000103@linux.intel.com> <1284735438.26423.81.camel@mulgrave.site> <1284741478.13344.154.camel@haakon2.linux-iscsi.org> <1284741704.13344.157.camel@haakon2.linux-iscsi.org> <1284745799.7280.155.camel@schen9-DESK> Content-Type: text/plain Date: Fri, 17 Sep 2010 11:21:36 -0700 Message-Id: <1284747696.13344.164.camel@haakon2.linux-iscsi.org> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-09-17 at 10:49 -0700, Tim Chen wrote: > On Fri, 2010-09-17 at 09:41 -0700, Nicholas A. Bellinger wrote: > > > > > > > > > What I was actually thinking of for the atomic is that we'd let it range > > > > [1..INT_MAX] so a zero was an indicator of no use of this. Then the > > > > actual code could become > > > > > > > > if (atomic_read(x)) { > > > > do { > > > > y = atomic_add_return(1, x); > > > > } while (y == 0); > > > > } > > > > > > The conversion of struct scsi_cmnd->serial_number to atomic_t and the > > > above code for scsi_cmd_get_serial() sounds perfectly reasonable to me. > > > > > > > Actually, that should be the conversion of struct > > Scsi_Host->cmd_serial_number to an atomic_t. AFAICT there is no reason > > for struct scsi_cmnd->serial_number needing to be an atomic_t. > > Just want to verify the hidden assumption we have here when the atomic > int Scsi_Host->cmd_serial_number counter overflow after increment. The > counter itself then becomes negative. We are assuming that when we do > type conversion back to unsigned long scsi_cmnd->serial_number, we will > get the right thing. > > So for 32-bit int, we expect if we start with 0x7fffffff in hex and the > expected sequence will be > > 2147483647 (int) -> 2147483647 (unsigned long) [0x7fffffff] > +1 > -2147483648 (int) -> 2147483648 (unsigned long) [0x80000000] > +1 > -2147483647 (int) -> 2147483649 (unsigned long) [0x80000001] > > If there is architecture where the above assumption is not true (which > I'm not aware of but just checking), then we should manually wrap the > atomic counter to 1 when counter overflow. > I was thinking about this as well, but I figured since jejb recommended it's usage for scsi_cmd_get_serial() that it would not be a problem. However I am not sure if he had keeping the struct scsi_cmnd->serial_number a 'unsigned long' that is done in the new v2 patches. James, is there any other consideration here wrt to atomic_t wrapping for scsi_cmd_get_serial() using a astruct Scsi_Host->cmd_serial_number assignment to an 'unsigned long' that I need to include in a v3 series..? --nab