linux-kernel - Re: [PATCH-v2 5/9] target: Convert se_portal_group->tpg_lun

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Date:	Fri, 22 May 2015 01:48:18 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Christoph Hellwig <hch@....de>
Cc:	"Nicholas A. Bellinger" <nab@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>,
	Sagi Grimberg <sagig@...lanox.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Chris Boot <bootc@...tc.net>
Subject: Re: [PATCH-v2 5/9] target: Convert se_portal_group->tpg_lun_list[]
 to RCU hlist

On Fri, 2015-05-22 at 10:31 +0200, Christoph Hellwig wrote:
> > This patch converts the fixed size se_portal_group->tpg_lun_list[]
> > to use modern RCU with hlist_head in order to support an arbitary
> > number of se_lun ports per target endpoint.
> > 
> > It includes dropping core_tpg_alloc_lun() from core_dev_add_lun(),
> > and calling it directly from target_fabric_make_lun() to allocate
> > a new se_lun.
> > 
> > Also add a new target_fabric_port_release() configfs item callback
> > to invoke kfree_rcu() to release memory during se_lun->lun_group
> > shutdown.
> > 
> > Also now that se_node_acl->lun_entry_hlist is using RCU, convert
> > existing tpg_lun_lock to struct mutex so core_tpg_add_node_to_devs()
> > can perform RCU updater logic without releasing ->tpg_lun_mutex.
> 
> Still doesn't explain why core_tpg_clear_object_luns also disappears.

It's duplicate logic in iscsi-target to delete active TPG LUNs.

Adding a comment to clarify the removal.

> 
> > +	hlist_for_each_entry_rcu(lun, &tpg->tpg_lun_hlist, link) {
> >  		if (lun->lun_status != TRANSPORT_LUN_STATUS_ACTIVE)
> >  			continue;
> 
> lun_status will always be active here as that's set and cleared at the
> same time as the list addition / removal.  Which means that lun_status
> should go away in this patch.
> 

Yes, thanks for the reminder.  Dropping lun_status now.

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