linux-kernel - Re: [PATCH] blk: improve order of bio handling in generic_make

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Message-ID: <b2a422af-b72f-df79-ba5b-239bde4d53cc@profitbricks.com>
Date:   Tue, 7 Mar 2017 09:49:59 +0100
From:   Jack Wang <jinpu.wang@...fitbricks.com>
To:     Jens Axboe <axboe@...nel.dk>, NeilBrown <neilb@...e.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Pavel Machek <pavel@....cz>, Mike Snitzer <snitzer@...hat.com>,
        Mikulas Patocka <mpatocka@...hat.com>
Subject: Re: [PATCH] blk: improve order of bio handling in
 generic_make_request()



On 06.03.2017 21:18, Jens Axboe wrote:
> On 03/05/2017 09:40 PM, NeilBrown wrote:
>> On Fri, Mar 03 2017, Jack Wang wrote:
>>>
>>> Thanks Neil for pushing the fix.
>>>
>>> We can optimize generic_make_request a little bit:
>>> - assign bio_list struct hold directly instead init and merge
>>> - remove duplicate code
>>>
>>> I think better to squash into your fix.
>>
>> Hi Jack,
>>  I don't object to your changes, but I'd like to see a response from
>>  Jens first.
>>  My preference would be to get the original patch in, then other changes
>>  that build on it, such as this one, can be added.  Until the core
>>  changes lands, any other work is pointless.
>>
>>  Of course if Jens wants a this merged before he'll apply it, I'll
>>  happily do that.
> 
> I like the change, and thanks for tackling this. It's been a pending
> issue for way too long. I do think we should squash Jack's patch
> into the original, as it does clean up the code nicely.
> 
> Do we have a proper test case for this, so we can verify that it
> does indeed also work in practice?
> 
Hi Jens,

I can trigger deadlock with in RAID1 with test below:

I create one md with one local loop device and one remote scsi
exported by SRP. running fio with mix rw on top of md, force_close
session on storage side. mdx_raid1 is wait on free_array in D state,
and a lot of fio also in D state in wait_barrier.

With the patch from Neil above, I can no longer trigger it anymore.

The discussion was in link below:
http://www.spinics.net/lists/raid/msg54680.html

Thanks,
Jack Wang