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SubjectRe: [PATCH 1/1] block: rework flush sequencing for blk-mq
On 03/08/2014 06:33 PM, Mike Snitzer wrote:
> On Sat, Mar 8, 2014 at 10:52 AM, Christoph Hellwig <hch@infradead.org> 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@suse.de +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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