Re: Question about expected behavior of terminate_rport_io() in fc_function_template

[Benjamin Block <bblock@linux.vnet.ibm.com>]

Hej Hannes,

thx for the short explanation.

On 23:05 Wed 23 Sep     , Hannes Reinecke wrote:
> On 09/23/2015 07:06 PM, Benjamin Block wrote:
> > Hello,
> > 
> > just a short question. If a low-level driver implements the function
> > `terminate_rport_io()` in `struct fc_function_template`, and it gets
> > called after IO failed, is the low-level driver expected to handle this
> > request synchronously or can it just schedule an action that is worked on
> > asynchronously to the call to the function?
> > 
> Actually, it doesn't matter, as 'terminate_rport_io()' should cause the
> driver to about outstanding commands. The main idea behind this is that
> the driver clears up any additional state it might have tacked onto the
> command. And calling '->done()', obviously.
> 
> Main goal is to have outstanding I/O returned to the upper layers, so
> that things like multipath can redirect outstanding I/O to other paths
> and facilitate quick failover.
>

Yeah, that is what I thought as well, after I read the initial patch
that introduced that function to the template and stack. Makes much more
sense then an implicit rule.

> 
> > Trouble is, we are seeing problems with SCSI-Commands being used by the
> > upper layers when we expect them to still be ours, after we got a call to
> > that function and didn't react upon it immediately. They do not contain
> > valid content anymore when they should.
> > 
> True; after terminate_rport_io() I/O should have been aborted.
> However, the SCSI layer really shouldn't reuse commands before ->done()
> has been invoked or the command itself has been aborted.
> 
> > I've looked into other implementations and it seems there are both
> > version, some LLDs explicitly wait upon completions of requests they
> > schedule and others just schedule work-items and return. That may
> > already be the answer, but I wanted to make sure I am not missing
> > something here. The documentation on it is not really existing, or I
> > missed it.
> > 
> As indicated, the driver is expected to call ->done() on outstanding
> commands when terminate_rport_io() is called.
> This smells more like an issue with the driver itself; if I were to
> guess I would think that some aborts are not handled correctly ...
> 
> But it's hard to know without details. Do you have some message log or
> something?
> 

It may well be that this is a problem in the driver. I am still working
on it, I have logs but those are very messy because the test load
involves LVM volumes with multiple LUNs and multipathing, and I am
trying to reduce it in order to be better able to debug it.



                                                    Beste Grüße / Best regards,
                                                      - Benjamin Block
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