target: Convert se_node_acl->device_list[] to RCU hlist

This patch converts se_node_acl->device_list[] table for mappedluns
to modern RCU hlist_head usage in order to support an arbitrary number
of node_acl lun mappings.

It converts transport_lookup_*_lun() fast-path code to use RCU read path
primitives when looking up se_dev_entry.  It adds a new hlist_head at
se_node_acl->lun_entry_hlist for this purpose.

For transport_lookup_cmd_lun() code, it works with existing per-cpu
se_lun->lun_ref when associating se_cmd with se_lun + se_device.
Also, go ahead and update core_create_device_list_for_node() +
core_free_device_list_for_node() to use ->lun_entry_hlist.

It also converts se_dev_entry->pr_ref_count access to use modern
struct kref counting, and updates core_disable_device_list_for_node()
to kref_put() and block on se_deve->pr_comp waiting for outstanding PR
special-case PR references to drop, then invoke kfree_rcu() to wait
for the RCU grace period to complete before releasing memory.

So now that se_node_acl->lun_entry_hlist fast path access uses RCU
protected pointers, go ahead and convert remaining non-fast path
RCU updater code using ->lun_entry_lock to struct mutex to allow
callers to block while walking se_node_acl->lun_entry_hlist.

Finally drop the left-over core_clear_initiator_node_from_tpg() that
originally cleared lun_access during se_node_acl shutdown, as post
RCU conversion it now becomes duplicated logic.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 17 insertions, 26 deletions

diff --git a/drivers/target/target_core_fabric_configfs.c b/drivers/target/target_core_fabric_configfs.c
index 6cb4828308e9..0939a5492c16 100644
--- a/drivers/target/target_core_fabric_configfs.c
+++ b/drivers/target/target_core_fabric_configfs.c
@@ -123,16 +123,16 @@ static int target_fabric_mappedlun_link(
 	 * which be will write protected (READ-ONLY) when
 	 * tpg_1/attrib/demo_mode_write_protect=1
 	 */
-	spin_lock_irq(&lacl->se_lun_nacl->device_list_lock);
-	deve = lacl->se_lun_nacl->device_list[lacl->mapped_lun];
-	if (deve->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS)
+	rcu_read_lock();
+	deve = target_nacl_find_deve(lacl->se_lun_nacl, lacl->mapped_lun);
+	if (deve)
 		lun_access = deve->lun_flags;
 	else
 		lun_access =
 			(se_tpg->se_tpg_tfo->tpg_check_prod_mode_write_protect(
 				se_tpg)) ? TRANSPORT_LUNFLAGS_READ_ONLY :
 					   TRANSPORT_LUNFLAGS_READ_WRITE;
-	spin_unlock_irq(&lacl->se_lun_nacl->device_list_lock);
+	rcu_read_unlock();
 	/*
 	 * Determine the actual mapped LUN value user wants..
 	 *
@@ -149,23 +149,13 @@ static int target_fabric_mappedlun_unlink(
 	struct config_item *lun_acl_ci,
 	struct config_item *lun_ci)
 {
-	struct se_lun *lun;
 	struct se_lun_acl *lacl = container_of(to_config_group(lun_acl_ci),
 			struct se_lun_acl, se_lun_group);
-	struct se_node_acl *nacl = lacl->se_lun_nacl;
-	struct se_dev_entry *deve = nacl->device_list[lacl->mapped_lun];
-	struct se_portal_group *se_tpg;
-	/*
-	 * Determine if the underlying MappedLUN has already been released..
-	 */
-	if (!deve->se_lun)
-		return 0;
-
-	lun = container_of(to_config_group(lun_ci), struct se_lun, lun_group);
-	se_tpg = lun->lun_sep->sep_tpg;
+	struct se_lun *lun = container_of(to_config_group(lun_ci),
+			struct se_lun, lun_group);
+	struct se_portal_group *se_tpg = lun->lun_sep->sep_tpg;
 
-	core_dev_del_initiator_node_lun_acl(se_tpg, lun, lacl);
-	return 0;
+	return core_dev_del_initiator_node_lun_acl(se_tpg, lun, lacl);
 }
 
 CONFIGFS_EATTR_STRUCT(target_fabric_mappedlun, se_lun_acl);
@@ -181,14 +171,15 @@ static ssize_t target_fabric_mappedlun_show_write_protect(
 {
 	struct se_node_acl *se_nacl = lacl->se_lun_nacl;
 	struct se_dev_entry *deve;
-	ssize_t len;
-
-	spin_lock_irq(&se_nacl->device_list_lock);
-	deve = se_nacl->device_list[lacl->mapped_lun];
-	len = sprintf(page, "%d\n",
-			(deve->lun_flags & TRANSPORT_LUNFLAGS_READ_ONLY) ?
-			1 : 0);
-	spin_unlock_irq(&se_nacl->device_list_lock);
+	ssize_t len = 0;
+
+	rcu_read_lock();
+	deve = target_nacl_find_deve(se_nacl, lacl->mapped_lun);
+	if (deve) {
+		len = sprintf(page, "%d\n",
+			(deve->lun_flags & TRANSPORT_LUNFLAGS_READ_ONLY) ? 1 : 0);
+	}
+	rcu_read_unlock();
 
 	return len;
 }