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

hch
2018-07-18T20:39:36Z

On Wed, Jul 18, 2018 at 09:56:50PM +0200, hch@lst.de wrote:
> On Fri, Jul 13, 2018 at 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.

So here is a quick attempt at the revert while also trying to keep
nvme working. Keith, Bart, Jianchao - does this looks reasonable
as a 4.18 band aid?