From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755239AbcJMLns (ORCPT ); Thu, 13 Oct 2016 07:43:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:55319 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754010AbcJMLnD (ORCPT ); Thu, 13 Oct 2016 07:43:03 -0400 Subject: Re: [PATCH v2 08/16] scsi: fc: implement kref backed reference counting To: Johannes Thumshirn , "Martin K . Petersen" References: <60854e8cdb8b2306d403973ff3759e3650e7d0de.1476276823.git.jthumshirn@suse.de> Cc: Christoph Hellwig , Linux Kernel Mailinglist , Linux SCSI Mailinglist , "James E.J. Bottomley" From: Hannes Reinecke Message-ID: Date: Thu, 13 Oct 2016 13:42:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <60854e8cdb8b2306d403973ff3759e3650e7d0de.1476276823.git.jthumshirn@suse.de> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12/2016 03:06 PM, Johannes Thumshirn wrote: > Implement kref backed reference counting instead of rolling our own. This > elimnates the need of the following fields in 'struct fc_bsg_job': > * ref_cnt > * state_flags > * job_lock > bringing us close to unification of 'struct fc_bsg_job' and 'struct bsg_job'. > > Signed-off-by: Johannes Thumshirn > --- > drivers/scsi/scsi_transport_fc.c | 38 +++++++++----------------------------- > include/scsi/scsi_transport_fc.h | 4 +--- > 2 files changed, 10 insertions(+), 32 deletions(-) > > diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c > index 96b3a2e..b0e28af 100644 > --- a/drivers/scsi/scsi_transport_fc.c > +++ b/drivers/scsi/scsi_transport_fc.c > @@ -3560,16 +3560,9 @@ fc_vport_sched_delete(struct work_struct *work) > * @job: fc_bsg_job that is to be torn down > */ > static void > -fc_destroy_bsgjob(struct fc_bsg_job *job) > +fc_destroy_bsgjob(struct kref *kref) > { > - unsigned long flags; > - > - spin_lock_irqsave(&job->job_lock, flags); > - if (job->ref_cnt) { > - spin_unlock_irqrestore(&job->job_lock, flags); > - return; > - } > - spin_unlock_irqrestore(&job->job_lock, flags); > + struct fc_bsg_job *job = container_of(kref, struct fc_bsg_job, kref); > > put_device(job->dev); /* release reference for the request */ > > @@ -3620,15 +3613,9 @@ EXPORT_SYMBOL_GPL(fc_bsg_jobdone); > static void fc_bsg_softirq_done(struct request *rq) > { > struct fc_bsg_job *job = rq->special; > - unsigned long flags; > - > - spin_lock_irqsave(&job->job_lock, flags); > - job->state_flags |= FC_RQST_STATE_DONE; > - job->ref_cnt--; > - spin_unlock_irqrestore(&job->job_lock, flags); > > blk_end_request_all(rq, rq->errors); > - fc_destroy_bsgjob(job); > + kref_put(&job->kref, fc_destroy_bsgjob); > } > > /** Hmm. blk_end_request_all() (potentially) triggers a recursion into all .end_io callbacks, which might end up doing god-knows-what. With some delays in doing so During that time we have no idea that bsg_softirq_done() is actually running, and we might clash with eg. timeouts or somesuch. Maybe it's an idea to move blk_end_request_all into the kref destroy callback; that way we're guaranteed to call it only once and would avoid this situation. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)