[libata] Use scsi_finish_command as completion function,

in our error handling thread callback.

This also exports scsi_finish_command in the SCSI layer.

Thanks much to James Bottomley and his patience, as this solution
was figured out.

drivers/scsi/libata-core.c

@@ -2005,6 +2005,14 @@ void ata_eng_timeout(struct ata_port *ap)
 		goto out;
 	}
 
+	/* hack alert!  We cannot use the supplied completion
+	 * function from inside the ->eh_strategy_handler() thread.
+	 * libata is the only user of ->eh_strategy_handler() in
+	 * any kernel, so the default scsi_done() assumes it is
+	 * not being called from the SCSI EH.
+	 */
+	qc->scsidone = scsi_finish_command;
+
 	switch (qc->tf.protocol) {
 	case ATA_PROT_DMA_READ:
 	case ATA_PROT_DMA_WRITE:

drivers/scsi/scsi.c

@@ -847,6 +847,7 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
 
 	cmd->done(cmd);
 }
+EXPORT_SYMBOL(scsi_finish_command);
 
 /*
  * Function:	scsi_adjust_queue_depth()

drivers/scsi/scsi_priv.h

@@ -77,7 +77,6 @@ extern int scsi_dispatch_cmd(struct scsi_cmnd *cmd);
 extern int scsi_setup_command_freelist(struct Scsi_Host *shost);
 extern void scsi_destroy_command_freelist(struct Scsi_Host *shost);
 extern void scsi_done(struct scsi_cmnd *cmd);
-extern void scsi_finish_command(struct scsi_cmnd *cmd);
 extern int scsi_retry_command(struct scsi_cmnd *cmd);
 extern int scsi_insert_special_req(struct scsi_request *sreq, int);
 extern void scsi_init_cmd_from_req(struct scsi_cmnd *cmd,

include/scsi/scsi_cmnd.h

@@ -159,5 +159,6 @@ struct scsi_cmnd {
 extern struct scsi_cmnd *scsi_get_command(struct scsi_device *, int);
 extern void scsi_put_command(struct scsi_cmnd *);
 extern void scsi_io_completion(struct scsi_cmnd *, unsigned int, unsigned int);
+extern void scsi_finish_command(struct scsi_cmnd *cmd);
 
 #endif /* _SCSI_SCSI_CMND_H */