Date:   Thu, 14 Sep 2023 08:03:53 +0200
From:   Donald Buczek <buczek@...gen.mpg.de>
To:     Dragan Stancevic <dragan@...ncevic.com>,
        Yu Kuai <yukuai1@...weicloud.com>, song@...nel.org
Cc:     guoqing.jiang@...ux.dev, it+raid@...gen.mpg.de,
        linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        msmith626@...il.com, "yangerkun@...wei.com" <yangerkun@...wei.com>
Subject: Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle"
 transition



On 9/13/23 16:16, Dragan Stancevic wrote:
> Hi Donald-
> 
> On 9/13/23 04:08, Donald Buczek wrote:
>> On 9/5/23 3:54 PM, Dragan Stancevic wrote:
>>> On 9/4/23 22:50, Yu Kuai wrote:
>>>> Hi,
>>>>
>>>> 在 2023/08/30 9:36, Yu Kuai 写道:
>>>>> Hi,
>>>>>
>>>>> 在 2023/08/29 4:32, Dragan Stancevic 写道:
>>>>>
>>>>>> Just a followup on 6.1 testing. I tried reproducing this problem for 5 days with 6.1.42 kernel without your patches and I was not able to reproduce it.
>>>>
>>>> oops, I forgot that you need to backport this patch first to reporduce
>>>> this problem:
>>>>
>>>> https://lore.kernel.org/all/20230529132037.2124527-2-yukuai1@huaweicloud.com/
>>>>
>>>> The patch fix the deadlock as well, but it introduce some regressions.
>>
>> We've just got an unplanned lock up on "check" to "idle" transition with 6.1.52 after a few hours on a backup server. For the last 2 1/2 years we used the patch I originally proposed with multiple kernel versions [1]. But this no longer seems to be valid or maybe its even destructive in combination with the other changes.
>>
>> But I totally lost track of the further development. As I understood, there are patches queue up in mainline, which might go into 6.1, too, but have not landed there which should fix the problem?
>>
>> Can anyone give me exact references to the patches I'd need to apply to 6.1.52, so that I could probably fix my problem and also test the patches for you those on production systems with a load which tends to run into that problem easily?
> 
> Here is a list of changes for 6.1:
> 
> e5e9b9cb71a0 md: factor out a helper to wake up md_thread directly
> f71209b1f21c md: enhance checking in md_check_recovery()
> 753260ed0b46 md: wake up 'resync_wait' at last in md_reap_sync_thread()
> 130443d60b1b md: refactor idle/frozen_sync_thread() to fix deadlock
> 6f56f0c4f124 md: add a mutex to synchronize idle and frozen in action_store()
> 64e5e09afc14 md: refactor action_store() for 'idle' and 'frozen'
> a865b96c513b Revert "md: unlock mddev before reap sync_thread in action_store"

Thanks!

I've put these patches on v6.1.52. I've started a script which transitions the three md-devices of a very active backup server through idle->check->idle every 6 minutes a few ours ago.  It went through ~400 iterations till now. No lock-ups so far.

LGTM !

   Donald

buczek@...e:~$ dmesg|grep "data-check of RAID array"|wc
     393    2820   18864
buczek@...e:~$ cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid6] [raid5] [raid4] [multipath]
md2 : active raid6 sdc[0] sdo[15] sdn[14] sdm[13] sdl[12] sdk[11] sdj[10] sdi[9] sdh[8] sdg[7] sdf[6] sde[5] sdd[4] sdr[3] sdq[2] sdp[1]
       109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
       [=========>...........]  check = 47.1% (3681799128/7813894144) finish=671.8min speed=102496K/sec
       bitmap: 0/59 pages [0KB], 65536KB chunk

md1 : active raid6 sdaa[0] sdz[15] sdy[14] sdx[13] sdw[12] sdv[11] sdu[10] sdt[16] sds[8] sdah[7] sdag[17] sdaf[5] sdae[4] sdad[3] sdac[2] sdab[1]
       109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
       [=======>.............]  check = 38.5% (3009484896/7813894144) finish=811.0min speed=98720K/sec
       bitmap: 0/59 pages [0KB], 65536KB chunk

md0 : active raid6 sdai[0] sdax[15] sdaw[16] sdav[13] sdau[12] sdat[11] sdas[10] sdar[9] sdaq[8] sdap[7] sdao[6] sdan[17] sdam[4] sdal[3] sdak[2] sdaj[1]
       109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
       [========>............]  check = 42.3% (3311789940/7813894144) finish=911.9min speed=82272K/sec
       bitmap: 6/59 pages [24KB], 65536KB chunk

unused devices: <none>





> 
> You can get them from the following tree:
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> 
> 
>>
>> Thanks
>>
>>    Donald
>>
>> [1]: https://lore.kernel.org/linux-raid/bc342de0-98d2-1733-39cd-cc1999777ff3@molgen.mpg.de/
>>
>>> Ha, jinx :) I was about to email you that I isolated that change with the testing over the weekend that made it more difficult to reproduce in 6.1 and that the original change must be reverted :)
>>>
>>>
>>>
>>>>
>>>> Thanks,
>>>> Kuai
>>>>
>>>>>>
>>>>>> It seems that 6.1 has some other code that prevents this from happening.
>>>>>>
>>>>>
>>>>> I see that there are lots of patches for raid456 between 5.10 and 6.1,
>>>>> however, I remember that I used to reporduce the deadlock after 6.1, and
>>>>> it's true it's not easy to reporduce, see below:
>>>>>
>>>>> https://lore.kernel.org/linux-raid/e9067438-d713-f5f3-0d3d-9e6b0e9efa0e@huaweicloud.com/
>>>>>
>>>>> My guess is that 6.1 is harder to reporduce than 5.10 due to some
>>>>> changes inside raid456.
>>>>>
>>>>> By the way, raid10 had a similiar deadlock, and can be fixed the same
>>>>> way, so it make sense to backport these patches.
>>>>>
>>>>> https://lore.kernel.org/r/20230529132037.2124527-5-yukuai1@huaweicloud.com
>>>>>
>>>>> Thanks,
>>>>> Kuai
>>>>>
>>>>>
>>>>>> On 5.10 I can reproduce it within minutes to an hour.
>>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>>
>>
>>
> 

-- 
Donald Buczek
buczek@...gen.mpg.de
Tel: +49 30 8413 1433

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