Re: Debugging scsi abort handling ?

[Hannes Reinecke <hare@suse.de>]

On 08/25/2014 01:15 PM, Paolo Bonzini wrote:
> Il 25/08/2014 12:28, Bart Van Assche ha scritto:
>>
>>  From SPC-4: "7.5.8 Control mode page [ ... ] A task aborted status (TAS)
>> bit set to zero specifies that aborted commands shall be terminated by
>> the device server without any response to the application client. A TAS
>> bit set to one specifies that commands aborted by the actions of an I_T
>> nexus other than the I_T nexus on which the command was received shall
>> be completed with TASK ABORTED status (see SAM-5)."
>
> Note the "aborted by the actions of an I_T nexus other than the I_T
> nexus on which the command was received".
>
> In practice, this means that TASK ABORTED should only happen if you use
> the CLEAR TASK SET tmf and TST is not set to 001b (i.e. _not_ to "per
> I_T nexus") in the Control mode page.  It should never happen for a pen
> drive.
>
> Setting TASK ABORTED aside, the important part is that an abort can do
> one of two things:
>
> - complete the command, and then eh_abort should return after the driver
> has noticed the completion and called the ->scsi_done callback for the
> Scsi_Cmnd*.
>
> - abort the command, and then the driver should never call the
> ->scsi_done callback for the Scsi_Cmnd*.
>
In practice we rely on the latter behaviour; when ->scsi_done is 
called while the command is under eh_abort _really bad things_
will happen.
As soon as eh_abort is called control is transferred back to the
SCSI midlayer, so any LLDD should never send completions for these
commands back to the midlayer.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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