target: Add generic active I/O shutdown logic

This patch adds the initial pieces of generic active I/O shutdown logic.
This is intended to be a 'opt-in' feature for fabric modules that
includes the following functions to provide a mechinism for fabric
modules to track se_cmd via se_session->sess_cmd_list:

*) target_get_sess_cmd() - Add se_cmd to sess->sess_cmd_list, called
   from fabric module incoming I/O path.
*) target_put_sess_cmd() - Check for completion or drop se_cmd from
   ->sess_cmd_list
*) target_splice_sess_cmd_list() - Splice active I/O list from
   ->sess_cmd_list to ->sess_wait_list, can called with HW fabric
   lock held.
*) target_wait_for_sess_cmds() - Walk ->sess_wait_list waiting on
   individual ->cmd_wait_comp.  Optional transport_wait_for_tasks()
   call.

target_splice_sess_cmd_list() is allowed to be called under HW fabric
lock, and performs the splice into se_sess->sess_wait_list and set
se_cmd->cmd_wait_set.  Then target_wait_for_sess_cmds() walks the list
waiting for individual target_put_sess_cmd() fabric callbacks to
complete.

It also adds TFO->check_release_cmd() to split the completion and memory
release calls, where a fabric module uses target_put_sess_cmd() to check
for I/O completion during session shutdown.  This is currently pushed out
into fabric modules as current fabric code may sleep here waiting for
TFO->check_stop_free() to complete in main response path, and because
target_wait_for_sess_cmds() calling TFO->release_cmd() to free fabric
descriptor memory directly.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>

3 files changed, 18 insertions, 1 deletions

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index d571bcfd16ad..dd245b68be5a 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -425,6 +425,9 @@ struct se_cmd {
         enum transport_state_table t_state;
         /* Transport specific error status */
         int                     transport_error_status;
+        /* Used to signal cmd->se_tfo->check_release_cmd() usage per cmd */
+        int                     check_release:1;
+        int                     cmd_wait_set:1;
         /* See se_cmd_flags_table */
         u32                     se_cmd_flags;
         u32                     se_ordered_id;
@@ -451,6 +454,8 @@ struct se_cmd {
         struct se_session       *se_sess;
         struct se_tmr_req       *se_tmr_req;
         struct list_head        se_queue_node;
+        struct list_head        se_cmd_list;
+        struct completion       cmd_wait_comp;
         struct target_core_fabric_ops *se_tfo;
         int (*transport_emulate_cdb)(struct se_cmd *);
         void (*transport_complete_callback)(struct se_cmd *);
@@ -558,12 +563,16 @@ struct se_node_acl {
 } ____cacheline_aligned;
 
 struct se_session {
+        int                     sess_tearing_down:1;
         u64                     sess_bin_isid;
         struct se_node_acl      *se_node_acl;
         struct se_portal_group *se_tpg;
         void                    *fabric_sess_ptr;
         struct list_head        sess_list;
         struct list_head        sess_acl_list;
+        struct list_head        sess_cmd_list;
+        struct list_head        sess_wait_list;
+        spinlock_t              sess_cmd_lock;
 } ____cacheline_aligned;
 
 struct se_device;
diff --git a/include/target/target_core_fabric_ops.h b/include/target/target_core_fabric_ops.h
index 04c591da0844..0256825f923d 100644
--- a/include/target/target_core_fabric_ops.h
+++ b/include/target/target_core_fabric_ops.h
@@ -52,6 +52,10 @@ struct target_core_fabric_ops {
          * Returning 0 will signal a descriptor has not been released.
          */
         int (*check_stop_free)(struct se_cmd *);
+        /*
+         * Optional check for active I/O shutdown
+         */
+        int (*check_release_cmd)(struct se_cmd *);
         void (*release_cmd)(struct se_cmd *);
         /*
          * Called with spin_lock_bh(struct se_portal_group->session_lock held.
diff --git a/include/target/target_core_transport.h b/include/target/target_core_transport.h
index d1b68c9ccb75..c16e9431dd01 100644
--- a/include/target/target_core_transport.h
+++ b/include/target/target_core_transport.h
@@ -164,12 +164,16 @@ extern bool target_stop_task(struct se_task *task, unsigned long *flags);
 extern int transport_generic_map_mem_to_cmd(struct se_cmd *cmd, struct scatterlist *, u32,
                                 struct scatterlist *, u32);
 extern int transport_clear_lun_from_sessions(struct se_lun *);
-extern void transport_wait_for_tasks(struct se_cmd *);
+extern bool transport_wait_for_tasks(struct se_cmd *);
 extern int transport_check_aborted_status(struct se_cmd *, int);
 extern int transport_send_check_condition_and_sense(struct se_cmd *, u8, int);
 extern void transport_send_task_abort(struct se_cmd *);
 extern void transport_release_cmd(struct se_cmd *);
 extern void transport_generic_free_cmd(struct se_cmd *, int);
+extern void target_get_sess_cmd(struct se_session *, struct se_cmd *);
+extern int target_put_sess_cmd(struct se_session *, struct se_cmd *);
+extern void target_splice_sess_cmd_list(struct se_session *);
+extern void target_wait_for_sess_cmds(struct se_session *, int);
 extern void transport_generic_wait_for_cmds(struct se_cmd *, int);
 extern void transport_do_task_sg_chain(struct se_cmd *);
 extern void transport_generic_process_write(struct se_cmd *);