linux-kernel - Re: Possible bug in DM-RAID.

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Message-ID: <562790FF.1060401@gmail.com>
Date:	Wed, 21 Oct 2015 09:19:59 -0400
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Linux-Kernel mailing list <linux-kernel@...r.kernel.org>,
	linux-raid@...r.kernel.org, dm-devel@...hat.org
Subject: Re: Possible bug in DM-RAID.

On 2015-10-20 11:12, Austin S Hemmelgarn wrote:
> I think I've stumbled upon a bug in DM-RAID.  The primary symptom is that when
> creating a new DM-RAID based device (using either LVM or dmsetup) in a RAID1
> configuration, it very quickly claims one by one that all of the disks failed
> except the first, and goes degraded.  When this happens on a given system, the
> disks always 'fail' in the reverse of the order of the mirror numbers.  All of
> the other RAID profiles work just fine.  Curiously, it also only seems to
> happen for 'big' devices (I haven't been able to determine exactly what the
> minimum size is, but I see it 100% of the time with 32G devices, never with 16G
> ones, and only intermittently with 24G).
OK, I've done some more experimentation, and have figured out that 
adjusting the sync region size from the default (and thus adjusting the 
bitmap size) can temporarily work around this.  If I adjust things so 
that the bitmap is less than 32 pages, then everything works fine, until 
I try to reboot, at which point the device either (in order of 
decreasing probability):
1. Fails just like I've outlined above.
2. Refuses to activate at all (if using LVM, you get some complaint 
about 'expected raid1 segment type, but got NULL' or 'reload ioctl on 
failed')
3. It works for a while, and then one of the first two things happens 
the next time I reboot.
>
> Here's what I got from dmesg when creating a 32G LVM volume that exhibited
> this issue:
> [66318.401295] device-mapper: raid: Superblocks created for new array
> [66318.450452] md/raid1:mdX: active with 2 out of 2 mirrors
> [66318.450467] Choosing daemon_sleep default (5 sec)
> [66318.450482] created bitmap (32 pages) for device mdX
> [66318.450495] attempt to access beyond end of device
> [66318.450501] dm-91: rw=13329, want=0, limit=8192
> [66318.450506] md: super_written gets error=-5, uptodate=0
> [66318.450513] md/raid1:mdX: Disk failure on dm-92, disabling device.
>                 md/raid1:mdX: Operation continuing on 1 devices.
> [66318.459815] attempt to access beyond end of device
> [66318.459819] dm-89: rw=13329, want=0, limit=8192
> [66318.459822] md: super_written gets error=-5, uptodate=0
> [66318.492852] attempt to access beyond end of device
> [66318.492862] dm-89: rw=13329, want=0, limit=8192
> [66318.492868] md: super_written gets error=-5, uptodate=0
> [66318.627183] mdX: bitmap file is out of date, doing full recovery
> [66318.714107] mdX: bitmap initialized from disk: read 3 pages, set 65536 of 65536 bits
> [66318.782045] RAID1 conf printout:
> [66318.782054]  --- wd:1 rd:2
> [66318.782061]  disk 0, wo:0, o:1, dev:dm-90
> [66318.782068]  disk 1, wo:1, o:0, dev:dm-92
> [66318.836598] RAID1 conf printout:
> [66318.836607]  --- wd:1 rd:2
> [66318.836614]  disk 0, wo:0, o:1, dev:dm-90
>
> And here's output for a 24G LVM volume that didn't display the issue.
> [66343.407954] device-mapper: raid: Superblocks created for new array
> [66343.479065] md/raid1:mdX: active with 2 out of 2 mirrors
> [66343.479078] Choosing daemon_sleep default (5 sec)
> [66343.479101] created bitmap (24 pages) for device mdX
> [66343.629329] mdX: bitmap file is out of date, doing full recovery
> [66343.677374] mdX: bitmap initialized from disk: read 2 pages, set 49152 of 49152 bits
>
> I'm using a lightly patched version of 4.2.3
> (the source can be found at https://github.com/ferroin/linux)
> but none of the patches I'm using come anywhere near anything in the block layer,
> let alone the DM/MD code.
>
> I've attempted to bisect this, although it got kind of complicated.  So far I've
> determined that the first commit that I see this issue on is d3b178a: md: Skip cluster setup for dm-raid
> Prior to that commit, I can't initialize any dm-raid devices due to the bug it fixes.
> I have not tested anything prior to d51e4fe (the merge commit that pulled in the md-cluster code),
> but I do distinctly remember that I did not see this issue in 3.19.
>
> I'll be happy to provide more info if needed.



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