[SCSI] improved eh timeout handler

When a command runs into a timeout we need to send an 'ABORT TASK'
TMF. This is typically done by the 'eh_abort_handler' LLDD callback.

Conceptually, however, this function is a normal SCSI command, so
there is no need to enter the error handler.

This patch implements a new scsi_abort_command() function which
invokes an asynchronous function scsi_eh_abort_handler() to
abort the commands via the usual 'eh_abort_handler'.

If abort succeeds the command is either retried or terminated,
depending on the number of allowed retries. However, 'eh_eflags'
records the abort, so if the retry would fail again the
command is pushed onto the error handler without trying to
abort it (again); it'll be cleared up from SCSI EH.

[hare: smatch detected stray switch fixed]
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi.c

@@ -297,6 +297,7 @@ struct scsi_cmnd *scsi_get_command(struct scsi_device *dev, gfp_t gfp_mask)
 
 		cmd->device = dev;
 		INIT_LIST_HEAD(&cmd->list);
+		INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
 		spin_lock_irqsave(&dev->list_lock, flags);
 		list_add_tail(&cmd->list, &dev->cmd_list);
 		spin_unlock_irqrestore(&dev->list_lock, flags);
@@ -353,6 +354,8 @@ void scsi_put_command(struct scsi_cmnd *cmd)
 	list_del_init(&cmd->list);
 	spin_unlock_irqrestore(&cmd->device->list_lock, flags);
 
+	cancel_delayed_work(&cmd->abort_work);
+
 	__scsi_put_command(cmd->device->host, cmd, &sdev->sdev_gendev);
 }
 EXPORT_SYMBOL(scsi_put_command);