scsi: target/core: Make ABORT and LUN RESET handling synchronous

Instead of invoking target driver callback functions from the context that
handles an abort or LUN RESET task management function, only set the abort
flag from that context and perform the actual abort handling from the
context of the regular command processing flow. This approach has the
advantage that the task management code becomes much easier to read and to
verify since the number of potential race conditions against the command
processing flow is strongly reduced.

This patch has been tested by running the following two shell commands
concurrently for about ten minutes for both the iSCSI and the SRP target
drivers ($dev is an initiator device node connected with storage provided
by the target driver under test):

 * fio with data verification enabled on a filesystem mounted on top of
   $dev.

 * while true; do sg_reset -d $dev; echo -n .; sleep .1; done

Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Disseldorp <ddiss@suse.de>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_internal.h

@@ -138,7 +138,6 @@ int	init_se_kmem_caches(void);
 void	release_se_kmem_caches(void);
 u32	scsi_get_new_index(scsi_index_t);
 void	transport_subsystem_check_init(void);
-int	transport_cmd_finish_abort(struct se_cmd *);
 unsigned char *transport_dump_cmd_direction(struct se_cmd *);
 void	transport_dump_dev_state(struct se_device *, char *, int *);
 void	transport_dump_dev_info(struct se_device *, struct se_lun *,
@@ -148,7 +147,6 @@ 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);
 void	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);
 bool	target_check_wce(struct se_device *dev);

drivers/target/target_core_tmr.c

@@ -171,11 +171,15 @@ void core_tmr_abort_task(
 
 		spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
 
-		cancel_work_sync(&se_cmd->work);
-		transport_wait_for_tasks(se_cmd);
+		/*
+		 * Ensure that this ABORT request is visible to the LU RESET
+		 * code.
+		 */
+		if (!tmr->tmr_dev)
+			WARN_ON_ONCE(transport_lookup_tmr_lun(tmr->task_cmd,
+						se_cmd->orig_fe_lun) < 0);
 
-		if (!transport_cmd_finish_abort(se_cmd))
-			target_put_sess_cmd(se_cmd);
+		target_put_cmd_and_wait(se_cmd);
 
 		printk("ABORT_TASK: Sending TMR_FUNCTION_COMPLETE for"
 				" ref_tag: %llu\n", ref_tag);
@@ -269,14 +273,28 @@ static void core_tmr_drain_tmr_list(
 			(preempt_and_abort_list) ? "Preempt" : "", tmr_p,
 			tmr_p->function, tmr_p->response, cmd->t_state);
 
-		cancel_work_sync(&cmd->work);
-		transport_wait_for_tasks(cmd);
-
-		if (!transport_cmd_finish_abort(cmd))
-			target_put_sess_cmd(cmd);
+		target_put_cmd_and_wait(cmd);
 	}
 }
 
+/**
+ * core_tmr_drain_state_list() - abort SCSI commands associated with a device
+ *
+ * @dev:       Device for which to abort outstanding SCSI commands.
+ * @prout_cmd: Pointer to the SCSI PREEMPT AND ABORT if this function is called
+ *             to realize the PREEMPT AND ABORT functionality.
+ * @tmr_sess:  Session through which the LUN RESET has been received.
+ * @tas:       Task Aborted Status (TAS) bit from the SCSI control mode page.
+ *             A quote from SPC-4, paragraph "7.5.10 Control mode page":
+ *             "A task aborted status (TAS) bit set to zero specifies that
+ *             aborted commands shall be terminated by the device server
+ *             without any response to the application client. A TAS bit set
+ *             to one specifies that commands aborted by the actions of an I_T
+ *             nexus other than the I_T nexus on which the command was
+ *             received shall be completed with TASK ABORTED status."
+ * @preempt_and_abort_list: For the PREEMPT AND ABORT functionality, a list
+ *             with registrations that will be preempted.
+ */
 static void core_tmr_drain_state_list(
 	struct se_device *dev,
 	struct se_cmd *prout_cmd,
@@ -351,18 +369,7 @@ static void core_tmr_drain_state_list(
 			 cmd->tag, (preempt_and_abort_list) ? "preempt" : "",
 			 cmd->pr_res_key);
 
-		/*
-		 * If the command may be queued onto a workqueue cancel it now.
-		 *
-		 * This is equivalent to removal from the execute queue in the
-		 * loop above, but we do it down here given that
-		 * cancel_work_sync may block.
-		 */
-		cancel_work_sync(&cmd->work);
-		transport_wait_for_tasks(cmd);
-
-		if (!transport_cmd_finish_abort(cmd))
-			target_put_sess_cmd(cmd);
+		target_put_cmd_and_wait(cmd);
 	}
 }
 

include/target/target_core_fabric.h

@@ -166,6 +166,7 @@ int	target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
 int	transport_handle_cdb_direct(struct se_cmd *);
 sense_reason_t	transport_generic_new_cmd(struct se_cmd *);
 
+void	target_put_cmd_and_wait(struct se_cmd *cmd);
 void	target_execute_cmd(struct se_cmd *cmd);
 
 int	transport_generic_free_cmd(struct se_cmd *, int);