linux-kernel - Re: [PATCH 09/12] target: Convert se_portal_group->tpg_lun

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Message-ID: <20150519064612.GA30172@lst.de>
Date:	Tue, 19 May 2015 08:46:12 +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>,
	Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: Re: [PATCH 09/12] target: Convert se_portal_group->tpg_lun_list[]
	to RCU hlist

On Tue, May 12, 2015 at 09:25:33AM +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@...ux-iscsi.org>
> 
> 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 call_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.

FYI, you can also kill ->lun_status with this as only allocated
se_lun structures will ever be on the list.
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