Re: iSCSI : Bridging missing CmdSNs and Abort I/O Error recovery

[Santosh Rao <santoshr@cup.hp.com>]

Julian,

I have re-read your previous answer and I may be missing something, but,
I don't see how it addresses my concern (?).

Per your mail :
"To abort safely a task for which the task abort answer is "Command Not
Received Yet" the initiator must issue another abort command on the same
connection as the original command unless this connection was logged out
in which case it may send it on any connection."

I'm pointing out that the above may not be sufficient since the issue
spans beyond that. If the target HAD received the command by the time it
received the task mgmt command on another connection, it would not
respond with "Command not received yet". In this case, the initiator
would not be required to re-send the Abort Task on the same connection
as the original command.

In such a scenario, if there were PDUs in-flight from target to
initiator on the original connection, these could arrive after the task
mgmt response [which is on the 2nd connection]. Such an Abort Task
cleanup does not reliably allow the initiator to free its task tag and
other resources, since PDUs for that task continue to arrive on the
original connection after the initiator has completed task clean-up
using Abort Task & released the task resources.

- Santosh





julian_satran@il.ibm.com wrote:
> 
> please reread carefully my previous answer. Julo
> 
> Santosh Rao <santoshr@cup.hp.com> on 09-05-2001 19:37:41
> 
> Please respond to Santosh Rao <santoshr@cup.hp.com>
> 
> To:   IPS Reflector <ips@ece.cmu.edu>
> cc:
> Subject:  Re: iSCSI : Bridging missing CmdSNs and Abort I/O Error recovery
> 
> > julian_satran@il.ibm.com wrote:
> 
> > > > We could add the RefCmdSN and it may help plug-in the hole but unless
> the
> > > > Abort is ussued on the same connection as the original command we
> can't
> > > be
> > > > sure that the old-one will not pop-up (as we enable ExpCmdSN to move
> on
> > > we
> > > > don't have even the 2**31-1 protection bracket :-)). Thus sending in
> > > > another nop/abort on the same connection is still required.
> > > >
> > > > To simplify the whole process I will:
> > > >
> > > >  a - add RefCmdSN to the Task Management
> > > >  b - add a command not received yet to the answers
> > > >
> > > >  c - add a part to 7 reading:
> > > >
> > > > 1.1  How to Abort Safely a Command that Was Not Received
> > > >
> > > >    To abort safely a task for which the task abort answer is "Command
> Not
> > > >    Received Yet" the initiator must issue another abort command on
> the
> > > same
> > > >    connection as the original command unless this connection was
> logged
> > > out
> > > >    in which case it may send it on any connection.
> 
> Julian,
> 
> The above may not be sufficient, since a requirement for the Abort Task
> completion is that both the initiator & target can safely re-use their
> task tags and other resources following completion of the Abort Task. If
> the Abort Task is sent on another connection than the connection used
> for the original command [& that connection has not been logged out],
> then, there may be some in-flight PDUs from the target to the initiator
> for that command on the connection.
> 
> Sending an Abort Task on another connection may cause the initiator to
> receive the Abort Task response indicating success on the other
> connection which then results in initiator freeing up its task tag and
> other resources used for that command. Thereafter, the stale PDUs on the
> original connection can show up at the initiator, causing problems.
> 
> I would suggest that Abort Task be always sent on the same connection as
> the command, unless the connection used for that command has been logged
> out. Not doing so implies the initiator cannot safely re-use its task
> tag and other resources that were tied up for that I/O.
> 
> Regards,
> Santosh
>  - santoshr.vcf
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