target: Add percpu refcounting for se_lun access

This patch adds percpu refcounting for se_lun access that allows the
association of an se_lun + se_cmd in transport_lookup_cmd_lun() to
occur without an extra list_head for tracking outstanding I/O during
se_lun shutdown.

This effectively changes se_lun shutdown logic to wait for outstanding
I/O percpu references to complete in transport_lun_remove_cmd() using
se_lun->lun_ref_comp, instead of explicitly draining the per se_lun
command list and waiting for individual se_cmd descriptor processing
to complete.

Cc: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

6 files changed, 45 insertions, 18 deletions

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index d90dbb0f1a69..569a3c7c9e5a 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -92,6 +92,9 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
                 se_cmd->pr_res_key = deve->pr_res_key;
                 se_cmd->orig_fe_lun = unpacked_lun;
                 se_cmd->se_cmd_flags |= SCF_SE_LUN_CMD;
+
+                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);
 
@@ -119,6 +122,9 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
                 se_cmd->se_lun = &se_sess->se_tpg->tpg_virt_lun0;
                 se_cmd->orig_fe_lun = 0;
                 se_cmd->se_cmd_flags |= SCF_SE_LUN_CMD;
+
+                percpu_ref_get(&se_lun->lun_ref);
+                se_cmd->lun_ref_active = true;
         }
 
         /* Directly associate cmd with se_dev */
@@ -134,10 +140,6 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u32 unpacked_lun)
                 dev->read_bytes += se_cmd->data_length;
         spin_unlock_irqrestore(&dev->stats_lock, flags);
 
-        spin_lock_irqsave(&se_lun->lun_cmd_lock, flags);
-        list_add_tail(&se_cmd->se_lun_node, &se_lun->lun_cmd_list);
-        spin_unlock_irqrestore(&se_lun->lun_cmd_lock, flags);
-
         return 0;
 }
 EXPORT_SYMBOL(transport_lookup_cmd_lun);
diff --git a/drivers/target/target_core_internal.h b/drivers/target/target_core_internal.h
index 889af4df8562..47b63b094cdc 100644
--- a/drivers/target/target_core_internal.h
+++ b/drivers/target/target_core_internal.h
@@ -100,7 +100,7 @@ int	transport_dump_vpd_assoc(struct t10_vpd *, unsigned char *, int);
 int     transport_dump_vpd_ident_type(struct t10_vpd *, unsigned char *, int);
 int     transport_dump_vpd_ident(struct t10_vpd *, unsigned char *, int);
 bool    target_stop_cmd(struct se_cmd *cmd, unsigned long *flags);
-int     transport_clear_lun_from_sessions(struct se_lun *);
+int     transport_clear_lun_ref(struct se_lun *);
 void    transport_send_task_abort(struct se_cmd *);
 sense_reason_t  target_cmd_size_check(struct se_cmd *cmd, unsigned int size);
 void    target_qf_do_work(struct work_struct *work);
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index ec992208dc55..f321af04ef03 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -634,6 +634,13 @@ int core_tpg_set_initiator_node_tag(
 }
 EXPORT_SYMBOL(core_tpg_set_initiator_node_tag);
 
+static void core_tpg_lun_ref_release(struct percpu_ref *ref)
+{
+        struct se_lun *lun = container_of(ref, struct se_lun, lun_ref);
+
+        complete(&lun->lun_ref_comp);
+}
+
 static int core_tpg_setup_virtual_lun0(struct se_portal_group *se_tpg)
 {
         /* Set in core_dev_setup_virtual_lun0() */
@@ -651,11 +658,18 @@ static int core_tpg_setup_virtual_lun0(struct se_portal_group *se_tpg)
         spin_lock_init(&lun->lun_acl_lock);
         spin_lock_init(&lun->lun_cmd_lock);
         spin_lock_init(&lun->lun_sep_lock);
+        init_completion(&lun->lun_ref_comp);
 
-        ret = core_tpg_post_addlun(se_tpg, lun, lun_access, dev);
+        ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release);
         if (ret < 0)
                 return ret;
 
+        ret = core_tpg_post_addlun(se_tpg, lun, lun_access, dev);
+        if (ret < 0) {
+                percpu_ref_cancel_init(&lun->lun_ref);
+                return ret;
+        }
+
         return 0;
 }
 
@@ -696,6 +710,7 @@ int core_tpg_register(
                 spin_lock_init(&lun->lun_acl_lock);
                 spin_lock_init(&lun->lun_cmd_lock);
                 spin_lock_init(&lun->lun_sep_lock);
+                init_completion(&lun->lun_ref_comp);
         }
 
         se_tpg->se_tpg_type = se_tpg_type;
@@ -816,10 +831,16 @@ int core_tpg_post_addlun(
 {
         int ret;
 
-        ret = core_dev_export(lun_ptr, tpg, lun);
+        ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release);
         if (ret < 0)
                 return ret;
 
+        ret = core_dev_export(lun_ptr, tpg, lun);
+        if (ret < 0) {
+                percpu_ref_cancel_init(&lun->lun_ref);
+                return ret;
+        }
+
         spin_lock(&tpg->tpg_lun_lock);
         lun->lun_access = lun_access;
         lun->lun_status = TRANSPORT_LUN_STATUS_ACTIVE;
@@ -833,7 +854,7 @@ static void core_tpg_shutdown_lun(
         struct se_lun *lun)
 {
         core_clear_lun_from_tpg(lun, tpg);
-        transport_clear_lun_from_sessions(lun);
+        transport_clear_lun_ref(lun);
 }
 
 struct se_lun *core_tpg_pre_dellun(
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 84747cc1aac0..ad143d7293ec 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -575,15 +575,11 @@ static int transport_cmd_check_stop_to_fabric(struct se_cmd *cmd)
 static void transport_lun_remove_cmd(struct se_cmd *cmd)
 {
         struct se_lun *lun = cmd->se_lun;
-        unsigned long flags;
 
-        if (!lun)
+        if (!lun || !cmd->lun_ref_active)
                 return;
 
-        spin_lock_irqsave(&lun->lun_cmd_lock, flags);
-        if (!list_empty(&cmd->se_lun_node))
-                list_del_init(&cmd->se_lun_node);
-        spin_unlock_irqrestore(&lun->lun_cmd_lock, flags);
+        percpu_ref_put(&lun->lun_ref);
 }
 
 void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
@@ -2537,21 +2533,23 @@ check_cond:
         spin_unlock_irqrestore(&lun->lun_cmd_lock, lun_flags);
 }
 
-static int transport_clear_lun_thread(void *p)
+static int transport_clear_lun_ref_thread(void *p)
 {
         struct se_lun *lun = p;
 
-        __transport_clear_lun_from_sessions(lun);
+        percpu_ref_kill(&lun->lun_ref);
+
+        wait_for_completion(&lun->lun_ref_comp);
         complete(&lun->lun_shutdown_comp);
 
         return 0;
 }
 
-int transport_clear_lun_from_sessions(struct se_lun *lun)
+int transport_clear_lun_ref(struct se_lun *lun)
 {
         struct task_struct *kt;
 
-        kt = kthread_run(transport_clear_lun_thread, lun,
+        kt = kthread_run(transport_clear_lun_ref_thread, lun,
                         "tcm_cl_%u", lun->unpacked_lun);
         if (IS_ERR(kt)) {
                 pr_err("Unable to start clear_lun thread\n");
diff --git a/drivers/target/target_core_xcopy.c b/drivers/target/target_core_xcopy.c
index 4d22e7d2adca..7a870f6add7b 100644
--- a/drivers/target/target_core_xcopy.c
+++ b/drivers/target/target_core_xcopy.c
@@ -579,6 +579,7 @@ static int target_xcopy_init_pt_lun(
         spin_lock_init(&pt_cmd->se_lun->lun_acl_lock);
         spin_lock_init(&pt_cmd->se_lun->lun_cmd_lock);
         spin_lock_init(&pt_cmd->se_lun->lun_sep_lock);
+        init_completion(&pt_cmd->se_lun->lun_ref_comp);
 
         pt_cmd->se_dev = se_dev;
 
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 22e752c4406d..4d16fd9330a6 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -499,6 +499,9 @@ struct se_cmd {
 
         /* backend private data */
         void                    *priv;
+
+        /* Used for lun->lun_ref counting */
+        bool                    lun_ref_active;
 };
 
 struct se_ua {
@@ -757,6 +760,8 @@ struct se_lun {
         struct se_port          *lun_sep;
         struct config_group     lun_group;
         struct se_port_stat_grps port_stat_grps;
+        struct completion       lun_ref_comp;
+        struct percpu_ref       lun_ref;
 };
 
 struct scsi_port_stats {