[RFC PATCH 3/3] blk-mq: Remove generation seqeunce

[hch@lst.de (hch@lst.de)]

On Fri, Jul 13, 2018@05:58:08PM -0600, Keith Busch wrote:
> Of the two you mentioned, yours is preferable IMO. While I appreciate
> Jianchao's detailed analysis, it's hard to take a proposal seriously
> that so colourfully calls everyone else "dangerous" while advocating
> for silently losing requests on purpose.
> 
> But where's the option that fixes scsi to handle hardware completions
> concurrently with arbitrary timeout software? Propping up that house of
> cards can't be the only recourse.

The important bit is that we need to fix this issue quickly.  We are
past -rc5 so I'm rather concerned about anything too complicated.

I'm not even sure SCSI has a problem with multiple completions happening
at the same time, but it certainly has a problem with bypassing
blk_mq_complete_request from the EH path.

I think we can solve this properly, but I also think we are way to late
in the 4.18 cycle to fix it properly.  For now I fear we'll just have
to revert the changes and try again for 4.19 or even 4.20 if we don't
act quickly enough.