[PATCH 05/12] target: Convert transport_lookup_*_lun to RCU reader

Nicholas A. Bellinger
2015-05-12T09:28:05Z

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch converts transport_lookup_*_lun() fast-path code to
use RCU read path primitives when looking up se_dev_entry. It
adds a new array of pointers in 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.

Finally, 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.

Cc: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
drivers/target/target_core_device.c | 60 +++++++++++++++++++++++--------------
drivers/target/target_core_pr.c | 1 +
drivers/target/target_core_tpg.c | 38 ++---------------------
include/target/target_core_base.h | 3 +-
4 files changed, 42 insertions(+), 60 deletions(-)

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index 1df14ce..36e7d13 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -59,17 +59,24 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
{
struct se_lun *se_lun = NULL;
struct se_session *se_sess = se_cmd->se_sess;
+ struct se_node_acl *nacl = se_sess->se_node_acl;
struct se_device *dev;
- unsigned long flags;
+ struct se_dev_entry *deve;

if (unpacked_lun >= TRANSPORT_MAX_LUNS_PER_TPG)
return TCM_NON_EXISTENT_LUN;

- spin_lock_irqsave(&se_sess->se_node_acl->device_list_lock, flags);
- se_cmd->se_deve = se_sess->se_node_acl->device_list[unpacked_lun];
- if (se_cmd->se_deve->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS) {
- struct se_dev_entry *deve = se_cmd->se_deve;
-
+ rcu_read_lock();
+ deve = target_nacl_find_deve(nacl, unpacked_lun);
+ if (deve && deve->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS) {
+ /*
+ * Make sure that target_enable_device_list_for_node()
+ * has not already cleared the RCU protected pointers.
+ */
+ if (!deve->se_lun) {
+ rcu_read_unlock();
+ goto check_lun;
+ }
deve->total_cmds++;

if ((se_cmd->data_direction == DMA_TO_DEVICE) &&
@@ -78,7 +85,7 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
" Access for 0x%08x\n",
se_cmd->se_tfo->get_fabric_name(),
unpacked_lun);
- spin_unlock_irqrestore(&se_sess->se_node_acl->device_list_lock, flags);
+ rcu_read_unlock();
return TCM_WRITE_PROTECTED;
}

@@ -96,8 +103,9 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
percpu_ref_get(&se_lun->lun_ref);
se_cmd->lun_ref_active = true;
}
- spin_unlock_irqrestore(&se_sess->se_node_acl->device_list_lock, flags);
+ rcu_read_unlock();

+check_lun:
if (!se_lun) {
/*
* Use the se_portal_group->tpg_virt_lun0 to allow for
@@ -146,25 +154,33 @@ int transport_lookup_tmr_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
struct se_dev_entry *deve;
struct se_lun *se_lun = NULL;
struct se_session *se_sess = se_cmd->se_sess;
+ struct se_node_acl *nacl = se_sess->se_node_acl;
struct se_tmr_req *se_tmr = se_cmd->se_tmr_req;
unsigned long flags;

if (unpacked_lun >= TRANSPORT_MAX_LUNS_PER_TPG)
return -ENODEV;

- spin_lock_irqsave(&se_sess->se_node_acl->device_list_lock, flags);
- se_cmd->se_deve = se_sess->se_node_acl->device_list[unpacked_lun];
- deve = se_cmd->se_deve;
-
- if (deve->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS) {
+ rcu_read_lock();
+ deve = target_nacl_find_deve(nacl, unpacked_lun);
+ if (deve && deve->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS) {
+ /*
+ * Make sure that target_enable_device_list_for_node()
+ * has not already cleared the RCU protected pointers.
+ */
+ if (!deve->se_lun) {
+ rcu_read_unlock();
+ goto check_lun;
+ }
se_tmr->tmr_lun = deve->se_lun;
se_cmd->se_lun = deve->se_lun;
se_lun = deve->se_lun;
se_cmd->pr_res_key = deve->pr_res_key;
se_cmd->orig_fe_lun = unpacked_lun;
}
- spin_unlock_irqrestore(&se_sess->se_node_acl->device_list_lock, flags);
+ rcu_read_unlock();

+check_lun:
if (!se_lun) {
pr_debug("TARGET_CORE[%s]: Detected NON_EXISTENT_LUN"
" Access for 0x%08x\n",
@@ -269,7 +285,7 @@ void core_update_device_list_access(
{
struct se_dev_entry *deve;

- spin_lock_irq(&nacl->lun_entry_lock);
+ mutex_lock(&nacl->lun_entry_mutex);
deve = target_nacl_find_deve(nacl, mapped_lun);
if (deve) {
if (lun_access & TRANSPORT_LUNFLAGS_READ_WRITE) {
@@ -280,7 +296,7 @@ void core_update_device_list_access(
deve->lun_flags |= TRANSPORT_LUNFLAGS_READ_ONLY;
}
}
- spin_unlock_irq(&nacl->lun_entry_lock);
+ mutex_unlock(&nacl->lun_entry_mutex);

synchronize_rcu();
}
@@ -345,7 +361,7 @@ int core_enable_device_list_for_node(
new->creation_time = get_jiffies_64();
new->attach_count++;

- spin_lock_irq(&nacl->device_list_lock);
+ mutex_lock(&nacl->lun_entry_mutex);
orig = target_nacl_find_deve(nacl, mapped_lun);
if (orig && orig->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS) {
BUG_ON(orig->se_lun_acl != NULL);
@@ -354,7 +370,7 @@ int core_enable_device_list_for_node(
rcu_assign_pointer(new->se_lun, lun);
rcu_assign_pointer(new->se_lun_acl, lun_acl);
hlist_add_head_rcu(&new->link, &nacl->lun_entry_hlist);
- spin_unlock_irq(&nacl->device_list_lock);
+ mutex_unlock(&nacl->lun_entry_mutex);

spin_lock_bh(&port->sep_alua_lock);
list_del(&orig->alua_port_list);
@@ -368,7 +384,7 @@ int core_enable_device_list_for_node(
rcu_assign_pointer(new->se_lun, lun);
rcu_assign_pointer(new->se_lun_acl, lun_acl);
hlist_add_head_rcu(&new->link, &nacl->lun_entry_hlist);
- spin_unlock_irq(&nacl->device_list_lock);
+ mutex_unlock(&nacl->lun_entry_mutex);

spin_lock_bh(&port->sep_alua_lock);
list_add_tail(&new->alua_port_list, &port->sep_alua_list);
@@ -393,10 +409,10 @@ int core_disable_device_list_for_node(
struct se_port *port = lun->lun_sep;
struct se_dev_entry *orig;

- spin_lock_irq(&nacl->device_list_lock);
+ mutex_lock(&nacl->lun_entry_mutex);
orig = target_nacl_find_deve(nacl, mapped_lun);
if (!orig) {
- spin_unlock_irq(&nacl->device_list_lock);
+ mutex_unlock(&nacl->lun_entry_mutex);
return 0;
}
/*
@@ -432,7 +448,7 @@ int core_disable_device_list_for_node(
orig->creation_time = 0;
orig->attach_count--;
hlist_del_rcu(&orig->link);
- spin_unlock_irq(&nacl->device_list_lock);
+ mutex_unlock(&nacl->lun_entry_mutex);

/*
* Fire off RCU callback to wait for any in process SPEC_I_PT=1
diff --git a/drivers/target/target_core_pr.c b/drivers/target/target_core_pr.c
index 8052d40..721b664 100644
--- a/drivers/target/target_core_pr.c
+++ b/drivers/target/target_core_pr.c
@@ -1066,6 +1066,7 @@ static void __core_scsi3_add_registration(
pr_reg_tmp->pr_reg_nacl, pr_reg_tmp,
register_type);
spin_unlock(&pr_tmpl->registration_lock);
+
/*
* Drop configfs group dependency reference from
* __core_scsi3_alloc_registration()
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index dbdd3e3..f9487e5 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -222,35 +222,6 @@ static void *array_zalloc(int n, size_t size, gfp_t flags)
return a;
}

-/* core_create_device_list_for_node():
- *
- *
- */
-static int core_create_device_list_for_node(struct se_node_acl *nacl)
-{
- struct se_dev_entry *deve;
- int i;
-
- nacl->device_list = array_zalloc(TRANSPORT_MAX_LUNS_PER_TPG,
- sizeof(struct se_dev_entry), GFP_KERNEL);
- if (!nacl->device_list) {
- pr_err("Unable to allocate memory for"
- " struct se_node_acl->device_list\n");
- return -ENOMEM;
- }
- for (i = 0; i < TRANSPORT_MAX_LUNS_PER_TPG; i++) {
- deve = nacl->device_list[i];
-
- atomic_set(&deve->ua_count, 0);
- atomic_set(&deve->pr_ref_count, 0);
- spin_lock_init(&deve->ua_lock);
- INIT_LIST_HEAD(&deve->alua_port_list);
- INIT_LIST_HEAD(&deve->ua_list);
- }
-
- return 0;
-}
-
static struct se_node_acl *target_alloc_node_acl(struct se_portal_group *tpg,
const unsigned char *initiatorname)
{
@@ -266,9 +237,8 @@ static struct se_node_acl *target_alloc_node_acl(struct se_portal_group *tpg,
INIT_HLIST_HEAD(&acl->lun_entry_hlist);
kref_init(&acl->acl_kref);
init_completion(&acl->acl_free_comp);
- spin_lock_init(&acl->device_list_lock);
spin_lock_init(&acl->nacl_sess_lock);
- spin_lock_init(&acl->lun_entry_lock);
+ mutex_init(&acl->lun_entry_mutex);
atomic_set(&acl->acl_pr_ref_count, 0);
if (tpg->se_tpg_tfo->tpg_get_default_depth)
acl->queue_depth = tpg->se_tpg_tfo->tpg_get_default_depth(tpg);
@@ -280,15 +250,11 @@ static struct se_node_acl *target_alloc_node_acl(struct se_portal_group *tpg,

tpg->se_tpg_tfo->set_default_node_attributes(acl);

- if (core_create_device_list_for_node(acl) < 0)
- goto out_free_acl;
if (core_set_queue_depth_for_node(tpg, acl) < 0)
- goto out_free_device_list;
+ goto out_free_acl;

return acl;

-out_free_device_list:
- core_free_device_list_for_node(acl, tpg);
out_free_acl:
kfree(acl);
return NULL;
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 6fb38df..3057eff 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -588,8 +588,7 @@ struct se_node_acl {
struct se_dev_entry **device_list;
struct se_session *nacl_sess;
struct se_portal_group *se_tpg;
- spinlock_t device_list_lock;
- spinlock_t lun_entry_lock;
+ struct mutex lun_entry_mutex;
spinlock_t nacl_sess_lock;
struct config_group acl_group;
struct config_group acl_attrib_group;
--
1.9.1