Re: SCSI eats error from flush failure during hot plug

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jun 19, 2014 at 11:05:59AM -0700, James Bottomley wrote:
> That's not really a good idea either ... I did think of it.  We'll end
> up with a cmd_type of REQ_TYPE_FS which because of REQ_FLUSH (or REQ_FUA
> or REQ_DISCARD or any number of other things) we have to treat as though
> it were REQ_TYPE_BLOCK_PC.  It's much better to tune handling
> expectations according to req->cmd_type because that's what we already
> do.  These commands are actually set up by our handlers, so it's up to
> us to mark the request type correctly.

Looking at the places where the SCSI midlayer cares about the request
type:

 - scsi_finish_command to call ->done for non-PC requests.  Given that
   we called into the driver to setup flush/discard/etc we should also
   call into the driver on request completion
 - scsi_eh_action: ditto for error handling
 - scsi_noretry_cmd: I don't see why we'd want to treat flush request
	as having an implicit failfast flag
 - scsi_io_completion: this mostly opts out of all kinds of error
	handling and retries, not really what we'd want either
 - scsi_unprep_fn: calls ->uninit_command only for !PC request,
   	so your patch introduces a leak for discard requests