From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH] libata: remove unlock+relock cycle in ata_scsi_queuecmd Date: Wed, 17 Nov 2010 11:01:13 +0100 Message-ID: <4CE3A7E9.3010009@kernel.org> References: <20101117062958.GA2894@havoc.gtf.org> <4CE38D70.4010507@garzik.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4CE38D70.4010507@garzik.org> Sender: linux-kernel-owner@vger.kernel.org To: Jeff Garzik Cc: Linus Torvalds , linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org, LKML List-Id: linux-scsi@vger.kernel.org Hello, Jeff, Linus. On 11/17/2010 09:08 AM, Jeff Garzik wrote: > Looking solely at the SCSI code (ie. ignoring LLD code), it seems > like the magic number zero for serial_number is signaling a boolean > condition "are we an EH command?" > > EH tests this at the very beginning of the abort/reset/explode error > handling sequence, presumably to avoid recursive EH invocations > (scsi_try_to_abort_cmd). > > So maybe an EH expert (Tejun?) can correct me here, but I think we > may be able to completely the lock/get-serial/unlock sequence from > libata, as long as scsi_init_cmd_errh() reliably sets an "I am an EH > command" flag. > > Would be nice if true... Yeah, it's actually nice (for once). libata doesn't use or care about scmd->serial_number at all. The SCSI EH path you mentioned above is not applicable as libata implements its eh_strategy_handler and SCSI only calls scsi_try_to_abort_cmd() for the default EH handler, scsi_unjam_host(). We'll need to test a bit to make sure everything is okay but I'm fairly certain removing it won't break anything fundamental. If something breaks at all, it would be some silly easy-to-fix thing. Thanks. -- tejun