Re: [PATCH 4/5] target: Fix multi-session dynamic se_node_acl double free OOPs

Christoph Hellwig
2017-02-07T23:07:06Z

On Tue, Feb 07, 2017 at 01:17:49PM +0000, Nicholas A. Bellinger wrote:
> - list_del(&acl->acl_list);
> + list_del_init(&acl->acl_list);

All these list_del_init changes don't make sense to me - the whole target
code never does a list_empty check on ->acl_list.

Looking further I think all nacls should be switched to the direct
free from the kref release callback scheme - there is no real need
to wait for freeing the nacl I think.

Untested patch below:

diff --git a/drivers/target/target_core_internal.h b/drivers/target/target_core_internal.h
index 9ab7090f7c83..96c38f30069d 100644
--- a/drivers/target/target_core_internal.h
+++ b/drivers/target/target_core_internal.h
@@ -152,6 +152,7 @@ void target_qf_do_work(struct work_struct *work);
bool target_check_wce(struct se_device *dev);
bool target_check_fua(struct se_device *dev);
void __target_execute_cmd(struct se_cmd *, bool);
+void target_put_nacl(struct se_node_acl *);

/* target_core_stat.c */
void target_stat_setup_dev_default_groups(struct se_device *);
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index d99752c6cd60..08738c87e5b0 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -197,7 +197,6 @@ static struct se_node_acl *target_alloc_node_acl(struct se_portal_group *tpg,
INIT_LIST_HEAD(&acl->acl_sess_list);
INIT_HLIST_HEAD(&acl->lun_entry_hlist);
kref_init(&acl->acl_kref);
- init_completion(&acl->acl_free_comp);
spin_lock_init(&acl->nacl_sess_lock);
mutex_init(&acl->lun_entry_mutex);
atomic_set(&acl->acl_pr_ref_count, 0);
@@ -370,21 +369,6 @@ void core_tpg_del_initiator_node_acl(struct se_node_acl *acl)
target_shutdown_sessions(acl);

target_put_nacl(acl);
- /*
- * Wait for last target_put_nacl() to complete in target_complete_nacl()
- * for active fabric session transport_deregister_session() callbacks.
- */
- wait_for_completion(&acl->acl_free_comp);
-
- core_tpg_wait_for_nacl_pr_ref(acl);
- core_free_device_list_for_node(acl, tpg);
-
- pr_debug("%s_TPG[%hu] - Deleted ACL with TCQ Depth: %d for %s"
- " Initiator Node: %s\n", tpg->se_tpg_tfo->get_fabric_name(),
- tpg->se_tpg_tfo->tpg_get_tag(tpg), acl->queue_depth,
- tpg->se_tpg_tfo->get_fabric_name(), acl->initiatorname);
-
- kfree(acl);
}

/* core_tpg_set_initiator_node_queue_depth():
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 1cadc9eefa21..72718283e553 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -453,19 +453,25 @@ ssize_t target_show_dynamic_sessions(struct se_portal_group *se_tpg, char *page)
}
EXPORT_SYMBOL(target_show_dynamic_sessions);

-static void target_complete_nacl(struct kref *kref)
+static void target_destroy_nacl(struct kref *kref)
{
struct se_node_acl *nacl = container_of(kref,
struct se_node_acl, acl_kref);
+ struct se_portal_group *se_tpg = nacl->se_tpg;

- complete(&nacl->acl_free_comp);
+ mutex_lock(&se_tpg->acl_node_mutex);
+ list_del(&nacl->acl_list);
+ mutex_unlock(&se_tpg->acl_node_mutex);
+
+ core_tpg_wait_for_nacl_pr_ref(nacl);
+ core_free_device_list_for_node(nacl, se_tpg);
+ kfree(nacl);
}

void target_put_nacl(struct se_node_acl *nacl)
{
- kref_put(&nacl->acl_kref, target_complete_nacl);
+ kref_put(&nacl->acl_kref, target_destroy_nacl);
}
-EXPORT_SYMBOL(target_put_nacl);

void transport_deregister_session_configfs(struct se_session *se_sess)
{
@@ -499,12 +505,39 @@ EXPORT_SYMBOL(transport_deregister_session_configfs);
void transport_free_session(struct se_session *se_sess)
{
struct se_node_acl *se_nacl = se_sess->se_node_acl;
+
/*
* Drop the se_node_acl->nacl_kref obtained from within
* core_tpg_get_initiator_node_acl().
*/
if (se_nacl) {
+ struct se_portal_group *se_tpg = se_nacl->se_tpg;
+ const struct target_core_fabric_ops *se_tfo = se_tpg->se_tpg_tfo;
+ unsigned long flags;
+
se_sess->se_node_acl = NULL;
+
+ /*
+ * Also determine if we need to drop the extra ->cmd_kref if
+ * it had been previously dynamically generated, and
+ * the endpoint is not caching dynamic ACLs.
+ */
+ mutex_lock(&se_tpg->acl_node_mutex);
+ if (se_nacl->dynamic_node_acl &&
+ !se_tfo->tpg_check_demo_mode_cache(se_tpg)) {
+ spin_lock_irqsave(&se_nacl->nacl_sess_lock, flags);
+ if (list_empty(&se_nacl->acl_sess_list))
+ stop = true;
+ spin_unlock_irqrestore(&se_nacl->nacl_sess_lock, flags);
+
+ if (stop)
+ list_del_init(&se_nacl->acl_list);
+ }
+ mutex_unlock(&se_tpg->acl_node_mutex);
+
+ if (stop)
+ target_put_nacl(se_nacl);
+
target_put_nacl(se_nacl);
}
if (se_sess->sess_cmd_map) {
@@ -518,16 +551,12 @@ EXPORT_SYMBOL(transport_free_session);
void transport_deregister_session(struct se_session *se_sess)
{
struct se_portal_group *se_tpg = se_sess->se_tpg;
- const struct target_core_fabric_ops *se_tfo;
- struct se_node_acl *se_nacl;
unsigned long flags;
- bool drop_nacl = false;

if (!se_tpg) {
transport_free_session(se_sess);
return;
}
- se_tfo = se_tpg->se_tpg_tfo;

spin_lock_irqsave(&se_tpg->session_lock, flags);
list_del(&se_sess->sess_list);
@@ -535,35 +564,8 @@ void transport_deregister_session(struct se_session *se_sess)
se_sess->fabric_sess_ptr = NULL;
spin_unlock_irqrestore(&se_tpg->session_lock, flags);

- /*
- * Determine if we need to do extra work for this initiator node's
- * struct se_node_acl if it had been previously dynamically generated.
- */
- se_nacl = se_sess->se_node_acl;
-
- mutex_lock(&se_tpg->acl_node_mutex);
- if (se_nacl && se_nacl->dynamic_node_acl) {
- if (!se_tfo->tpg_check_demo_mode_cache(se_tpg)) {
- list_del(&se_nacl->acl_list);
- drop_nacl = true;
- }
- }
- mutex_unlock(&se_tpg->acl_node_mutex);
-
- if (drop_nacl) {
- core_tpg_wait_for_nacl_pr_ref(se_nacl);
- core_free_device_list_for_node(se_nacl, se_tpg);
- se_sess->se_node_acl = NULL;
- kfree(se_nacl);
- }
pr_debug("TARGET_CORE[%s]: Deregistered fabric_sess\n",
se_tpg->se_tpg_tfo->get_fabric_name());
- /*
- * If last kref is dropping now for an explicit NodeACL, awake sleeping
- * ->acl_free_comp caller to wakeup configfs se_node_acl->acl_group
- * removal context from within transport_free_session() code.
- */
-
transport_free_session(se_sess);
}
EXPORT_SYMBOL(transport_deregister_session);
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 43edf82e54ff..edad452c3c25 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -557,7 +557,6 @@ struct se_node_acl {
struct config_group acl_fabric_stat_group;
struct list_head acl_list;
struct list_head acl_sess_list;
- struct completion acl_free_comp;
struct kref acl_kref;
};

diff --git a/include/target/target_core_fabric.h b/include/target/target_core_fabric.h
index 358041bad1da..1c417731b63d 100644
--- a/include/target/target_core_fabric.h
+++ b/include/target/target_core_fabric.h
@@ -125,7 +125,6 @@ void transport_register_session(struct se_portal_group *,
struct se_node_acl *, struct se_session *, void *);
ssize_t target_show_dynamic_sessions(struct se_portal_group *, char *);
void transport_free_session(struct se_session *);
-void target_put_nacl(struct se_node_acl *);
void transport_deregister_session_configfs(struct se_session *);
void transport_deregister_session(struct se_session *);