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

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Message-ID: <20150522083113.GC24640@lst.de>
Date:	Fri, 22 May 2015 10:31:13 +0200
From:	Christoph Hellwig <hch@....de>
To:	"Nicholas A. Bellinger" <nab@...erainc.com>
Cc:	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>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagig@...lanox.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Chris Boot <bootc@...tc.net>
Subject: Re: [PATCH-v2 5/9] target: Convert se_portal_group->tpg_lun_list[]
	to RCU hlist

> 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.

> +	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.

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