Re: [PATCH 1/1] block: rework flush sequencing for blk-mq

[Hannes Reinecke]

On 03/08/2014 06:33 PM, Mike Snitzer wrote:
> On Sat, Mar 8, 2014 at 10:52 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> > On Fri, Mar 07, 2014 at 03:45:09PM -0500, Jeff Moyer wrote:
> > > Hi, Christoph,
> > >
> > > Did you mean to switch from list_add to list_add_tail?  That seems like
> > > a change that warrants mention.
> >
> > No, that wasn't intentional and should be fixed.  Btw, there was another
> > issue with that commit, in that dm-multipath also needs to allocate
> > ->flush_rq.  I saw a patch from Hannes fixing it in the SuSE tree, and
> > would really love to see him submit that for mainline as well.
>
> Ugh, rq-based DM calls blk_init_allocated_queue.. (ah, looks like best
> to move q->flush_rq allocation from blk_init_queue_node to
> blk_alloc_queue_node?).  Anyway, this all makes sense given the
> crashes we've been dealing with.. we couldn't immediately understand
> how the q->flush_rq would be NULL... grr.  I guess I should've checked
> with you sooner.  I reverted commit 1874198 "blk-mq: rework flush
> sequencing logic" from RHEL7 just yesterday because we were seeing
> crashes on flush with dm-mpath.  But can easily re-apply for RHEL7.1
> (since the request_queue's embedded flush_rq takes up so much space we
> get ample kABI padding).
>
> Not overly proud of the revert, but I deemed easier to revert than
> hunt down the fix given RHEL7 won't actually be providing any blk-mq
> enabled drivers.  That'll change for RHEL7.1.
>
> > Unfortunately SuSE seems to have lots of block and dm fixes and even
> > features that they don't submit upstream.
>
> Yeah, it is certainly disturbing.  No excuse for sitting on fixes like this.
>
> Hannes, _please_ get this dm-mpath flush_rq fix for 3.14 posted ASAP.
> Jens or I will need to get it to Linus next week.
Hey, calm down.
I've made the fix just two days ago. And was quite surprised that I've 
been the first hitting that; should've crashed for everybody using 
dm-multipath.
And given the pushback I've gotten recently from patches I would have 
thought that it would work for most users; sure the author would've done 
due diligence on the original patchset ...
Plus I've gotten the reports from S/390, so I put it down to mainframe 
weirdness.

BTW, it not _my_ decision to sit on tons of SUSE specific patches.
I really try to get things upstream. But I cannot do more than sending 
patches upstream, answer patiently any questions, and redo the patchset.
Which I did. Frequently, But, alas, it's up to the maintainer to apply 
them. And I can only ask and hope. The usual story...

I'll be sending the patch soon, Monday at latest.

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
hare@xxxxxxx			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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