linux-kernel - Re: [PATCH-v2 2/9] target/pr: Use atomic bitop for se_dev_entry->pr

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Message-ID: <555F0107.6030102@sandisk.com>
Date:	Fri, 22 May 2015 12:12:23 +0200
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	"Nicholas A. Bellinger" <nab@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>
CC:	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>
Subject: Re: [PATCH-v2 2/9] target/pr: Use atomic bitop for se_dev_entry->pr_reg
 reservation check

On 05/22/15 08:11, Nicholas A. Bellinger wrote:
> diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
> index e2c0eaf..def5bc8 100644
> --- a/include/target/target_core_base.h
> +++ b/include/target/target_core_base.h
> @@ -638,7 +638,6 @@ struct se_lun_acl {
>   };
>
>   struct se_dev_entry {
> -	bool			def_pr_registered;
>   	/* See transport_lunflags_table */
>   	u32			lun_flags;
>   	u32			mapped_lun;
> @@ -655,7 +654,8 @@ struct se_dev_entry {
>   	struct se_node_acl	*se_node_acl;
>   	struct se_lun_acl __rcu	*se_lun_acl;
>   	spinlock_t		ua_lock;
> -	struct se_lun		*se_lun;
> +	struct se_lun __rcu	*se_lun;
> +	unsigned long		pr_reg;
>   	struct list_head	alua_port_list;
>   	struct list_head	ua_list;
>   	struct hlist_node	link;

Hello Nic,

This change causes the "se_lun = deve->se_lun" assignment in 
transport_lookup_cmd_lun() to assign an RCU pointer to a non-RCU 
pointer. Shouldn't such an assignment be protected via rcu_dereference() ?

Thanks,

Bart.
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