linux-kernel - Re: [PATCH-v2 4/4] target: Obtain se_node_acl->acl_kref during get_initiator_node

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Date:	Wed, 13 Jan 2016 00:38:08 -0800
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>,
	lkml <linux-kernel@...r.kernel.org>,
	Sagi Grimberg <sagig@...lanox.com>,
	Hannes Reinecke <hare@...e.de>,
	Andy Grover <agrover@...hat.com>,
	Vasu Dev <vasu.dev@...ux.intel.com>, Vu Pham <vu@...lanox.com>
Subject: Re: [PATCH-v2 4/4] target: Obtain se_node_acl->acl_kref during
 get_initiator_node_acl

On Wed, 2016-01-13 at 09:15 +0100, Christoph Hellwig wrote:
> On Wed, Jan 13, 2016 at 12:00:28AM -0800, Nicholas A. Bellinger wrote:
> > diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
> > index 52ae8ba..62f02ea 100644
> > --- a/drivers/target/target_core_tpg.c
> > +++ b/drivers/target/target_core_tpg.c
> > @@ -75,16 +75,9 @@ struct se_node_acl *core_tpg_get_initiator_node_acl(
> >         unsigned char *initiatorname)
> >  {
> >         struct se_node_acl *acl;
> > -       /*
> > -        * Obtain the acl_kref now, which will be dropped upon the
> > -        * release of se_sess memory within transport_free_session().
> > -        */
> > +
> >         mutex_lock(&tpg->acl_node_mutex);
> >         acl = __core_tpg_get_initiator_node_acl(tpg, initiatorname);
> > -       if (acl) {
> > -               if (!kref_get_unless_zero(&acl->acl_kref))
> > -                       acl = NULL;
> > -       }
> 
> nah, please keep the kref_get_unless_zero here, it's needed.  It's
> just the misleding comment I was complaining about :)

Ok.  How about the following comment instead..?

diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 62f02ea..1984bb2 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -75,9 +75,21 @@ struct se_node_acl *core_tpg_get_initiator_node_acl(
        unsigned char *initiatorname)
 {
        struct se_node_acl *acl;
-
+       /*
+        * Obtain se_node_acl->acl_kref using fabric driver provided
+        * initiatorname[] during node acl endpoint lookup driven by
+        * new se_session login.
+        *
+        * The reference is held until se_session shutdown -> release
+        * occurs via fabric driver invoked transport_deregister_session()
+        * or transport_free_session() code.
+        */

> 
> > @@ -3435,10 +3436,14 @@ iscsit_build_sendtargets_response(struct iscsi_cmd *cmd,
> >  
> >                         if ((tpg->tpg_attrib.generate_node_acls == 0) &&
> >                             (tpg->tpg_attrib.demo_mode_discovery == 0) &&
> > -                           (!core_tpg_get_initiator_node_acl(&tpg->tpg_se_tpg,
> > -                               cmd->conn->sess->sess_ops->InitiatorName))) {
> > +                           (!(se_acl = core_tpg_get_initiator_node_acl(&tpg->tpg_se_tpg,
> > +                               cmd->conn->sess->sess_ops->InitiatorName)))) {
> >                                 continue;
> >                         }
> > +                       if (se_acl) {
> > +                               target_put_nacl(se_acl);
> > +                               se_acl = NULL;
> > +                       }
> 
> 
> Seems like with the current code we don't need to keep the ACL,
> so a new helper like:
> 
> bool target_tpg_has_node_acl(struct se_portal_group *tpg,
> 	const char *initiatorname)
> {
> 	struct se_node_acl *acl;
> 
> 	acl = core_tpg_get_initiator_node_acl(tpg, initiatorname);
> 	if (acl) {
> 		target_put_nacl(se_acl);
> 		return true;
> 	}
> 
> 	return false;
> }
> 
> or fully open coded as:
> 
> bool target_tpg_has_node_acl(struct se_portal_group *tpg,
> 		 const char *initiatorname)
> {
> 	struct se_node_acl *acl;
> 	bool found = false;
> 
> 	mutex_lock(&tpg->acl_node_mutex);
> 	list_for_each_entry(acl, &tpg->acl_node_list, acl_list) {
> 		if (!strcmp(acl->initiatorname, initiatorname)) {
> 			found = true;
> 			break;
> 		}
> 	}
> 	mutex_unlock(&tpg->acl_node_mutex);
> 
> 	return found;
> }
> 
> might be better to keep the code readable.

Seems reasonable.  Adding this instead.