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>

1 files changed, 5 insertions, 0 deletions

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 {