[PATCH 1/3] target: Add support for TMR percpu reference counting

[Nicholas A. Bellinger]

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

This patch introduces TMR percpu reference counting using
se_lun->lun_ref in transport_lookup_tmr_lun(), following
how existing non TMR per se_lun reference counting works
within transport_lookup_cmd_lun().

It also adds explicit transport_lun_remove_cmd() calls to
drop the reference in the three tmr related locations that
invoke transport_cmd_check_stop_to_fabric();

   - target_tmr_work() during normal ->queue_tm_rsp()
   - target_complete_tmr_failure() during error ->queue_tm_rsp()
   - transport_generic_handle_tmr() during early failure

Also, note the exception paths in transport_generic_free_cmd()
and transport_cmd_finish_abort() already check SCF_SE_LUN_CMD,
and will invoke transport_lun_remove_cmd() when necessary.

Cc: Himanshu Madhani <himanshu.madh...@cavium.com>
Cc: Quinn Tran <quinn.t...@cavium.com>
Cc: Mike Christie <mchri...@redhat.com>
Cc: Hannes Reinecke <h...@suse.com>
Cc: Christoph Hellwig <h...@lst.de>
Signed-off-by: Nicholas Bellinger <n...@linux-iscsi.org>
---
 drivers/target/target_core_device.c    | 14 ++++++++++----
 drivers/target/target_core_transport.c |  3 +++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/target/target_core_device.c 
b/drivers/target/target_core_device.c
index 8f0e0e3..11c80c4 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -168,11 +168,20 @@ int transport_lookup_tmr_lun(struct se_cmd *se_cmd, u64 
unpacked_lun)
        rcu_read_lock();
        deve = target_nacl_find_deve(nacl, unpacked_lun);
        if (deve) {
-               se_cmd->se_lun = rcu_dereference(deve->se_lun);
                se_lun = rcu_dereference(deve->se_lun);
+
+               if (!percpu_ref_tryget_live(&se_lun->lun_ref)) {
+                       se_lun = NULL;
+                       goto out_unlock;
+               }
+
+               se_cmd->se_lun = rcu_dereference(deve->se_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;
+               se_cmd->lun_ref_active = true;
        }
+out_unlock:
        rcu_read_unlock();
 
        if (!se_lun) {
@@ -182,9 +191,6 @@ int transport_lookup_tmr_lun(struct se_cmd *se_cmd, u64 
unpacked_lun)
                        unpacked_lun);
                return -ENODEV;
        }
-       /*
-        * XXX: Add percpu se_lun->lun_ref reference count for TMR
-        */
        se_cmd->se_dev = rcu_dereference_raw(se_lun->lun_se_dev);
        se_tmr->tmr_dev = rcu_dereference_raw(se_lun->lun_se_dev);
 
diff --git a/drivers/target/target_core_transport.c 
b/drivers/target/target_core_transport.c
index f16a789..83bfc97 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1588,6 +1588,7 @@ static void target_complete_tmr_failure(struct 
work_struct *work)
        se_cmd->se_tmr_req->response = TMR_LUN_DOES_NOT_EXIST;
        se_cmd->se_tfo->queue_tm_rsp(se_cmd);
 
+       transport_lun_remove_cmd(se_cmd);
        transport_cmd_check_stop_to_fabric(se_cmd);
 }
 
@@ -3199,6 +3200,7 @@ static void target_tmr_work(struct work_struct *work)
        cmd->se_tfo->queue_tm_rsp(cmd);
 
 check_stop:
+       transport_lun_remove_cmd(cmd);
        transport_cmd_check_stop_to_fabric(cmd);
 }
 
@@ -3221,6 +3223,7 @@ int transport_generic_handle_tmr(
                pr_warn_ratelimited("handle_tmr caught CMD_T_ABORTED TMR %d"
                        "ref_tag: %llu tag: %llu\n", cmd->se_tmr_req->function,
                        cmd->se_tmr_req->ref_task_tag, cmd->tag);
+               transport_lun_remove_cmd(cmd);
                transport_cmd_check_stop_to_fabric(cmd);
                return 0;
        }
-- 
1.9.1