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 d571bcfd16a..dd245b68be5 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 04c591da084..0256825f923 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 d1b68c9ccb7..c16e9431dd0 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 *);