iSCSI: aborting an immediate command with ABORT TASK

["Tony Battersby" <tonyb@cybernetics.com>]

It seems that an initiator attempting to abort an immediate command may
inadvertently cause the next non-immediate command to be aborted instead.
For example,

Initiator sends an immediate command "A" with CmdSN 10.
Initiator sends a non-immediate command "B" with CmdSN 10.
Initiator sends an immediate ABORT TASK command "C" with CmdSN 11 to abort
command "A" (RefCmdSN == 10, Referenced Task Tag == Initiator Task Tag of
"A").

If the target either:
1) Receives "C" before "A" or "B", OR
2) Receives "C" before "B" but after executing and freeing "A",

...then the target will not have a matching task for the abort in its queue,
and will consider CmdSN 10 received because it is inside the valid CmdSN
window.  If the target then receives "B", it will silently ignore the
command because it is outside the valid CmdSN window.  This is obviously not
what the initiator was trying to accomplish.

This problem could be solved by adding a flag to the PDU for the ABORT TASK
command to indicate if the task to be aborted is immediate or non-immediate.
If the target does not have a matching task and the RefCmdSN is inside the
valid command window, then the target should consider the CmdSN received
only if the flag indicates that the task to be aborted is non-immediate.

-----------------------

One other thing: for draft 16, I recommend that the the following phrase:
"... (i.e., with CmdSN not higher than the task management command CmdSN)
..."
in section 9.5.1 be changed to:
"... (i.e., with CmdSN lower than the task management command CmdSN) ...".
This is for consistency with another sentence earlier in the same paragraph.


Anthony J. Battersby
Cybernetics