Ext4 and scsi commands resubmission

[torn5 <torn5@shiftmail.org>]

Hello all,

in open-iscsi, when network connectivity is lost, scsi commands that 
were in-flight at the moment of disconnection are failed to the SCSI layer.
These get resubmitted up to 5 times by the SCSI layer (or so is written 
in the open-iscsi docs) and after that they are held in the queue 
(device "blocked") until the network connection is restored.

Now the question is: when SCSI resubmits commands to a device, I suppose 
they go to the end of the queue for the device, and not at the head like 
they were. Am I right?
How do filesystems, and in particular ext4, react to that?
I suppose the ordering goes awry, barriers cannot succeed in this way, 
especially if they were submitted as real SCSI barriers (i.e. without 
using flush + command + flush workaround)

Thank you