Re: Can anyone boot a system using btrfs root with linux 3.14 or newer?

From: Chris Mason <clm@fb.com>
To: Chris Murphy <lists@colorremedies.com>, Marc MERLIN <marc@merlins.org>
Cc: "Пламен Петров" <plamen@petrovi.no-ip.info>, linux-btrfs@vger.kernel.org
Subject: Re: Can anyone boot a system using btrfs root with linux 3.14 or newer?
Date: Thu, 24 Apr 2014 20:08:28 -0400	[thread overview]
Message-ID: <5359A77C.70209@fb.com> (raw)
In-Reply-To: <F6EDB160-FCC5-4D1C-A5A8-AAADE5C803F6@colorremedies.com>

On 04/24/2014 08:04 PM, Chris Murphy wrote:
>
> On Apr 24, 2014, at 5:07 PM, Marc MERLIN <marc@merlins.org> wrote:
>>
>>
>> In 3.14 the device shows up before btrfs is loaded:
>> sd 2:0:0:0: [sda] Cache data unavailable
>> sd 2:0:0:0: [sda] Assuming drive cache: write through
>> sd 2:0:0:0: [sda] Attached SCSI disk
>> (...)
>> Btrfs loaded
>
> Same for me though, and I can boot.
>
> [    0.693215] ata1.00: ATA-6: VBOX HARDDISK, 1.0, max UDMA/133
> [    0.693799] ata1.00: 167772160 sectors, multi 128: LBA48 NCQ (depth 31/32)
> [    0.694153] ata1.00: configured for UDMA/133
> [    0.695475] scsi 0:0:0:0: Direct-Access     ATA      VBOX HARDDISK    1.0  PQ: 0 ANSI: 5
> [    0.699386] sd 0:0:0:0: [sda] 167772160 512-byte logical blocks: (85.8 GB/80.0 GiB)
> [    0.699443] sd 0:0:0:0: Attached scsi generic sg0 type 0
> [    0.700604] sd 0:0:0:0: [sda] Write Protect is off
> [    0.701151] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
> [    0.701187] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
> [    0.707841]  sda: sda1 sda2 sda3
> [    0.709846] sd 0:0:0:0: [sda] Attached SCSI disk
> (…)
> [    2.380090] bio: create slab <bio-1> at 1
> [    2.384645] Btrfs loaded
>
> So I don't think the order is it. The biggest difference I'm seeing between the 3.13.11 and 3.14.1 dmesg's provided:
>
> 3.13.11:
> [    1.861740] bio: create slab <bio-1> at 1
> [    1.863389] Btrfs loaded
>
> 3.14.1:
> [    3.949312] bio: create slab <bio-1> at 1
> [    3.950942] Btrfs loaded
>
> It's happening much later, and it's right at this point VFS complains:
> [    4.182603] VFS: Cannot open root device "sda2" or unknown-block(8,2): error -38
>
> The 8,2 message is consistent with the kernel not knowing what file system sda2 is. Seems like it's saying "I see sda2, I know you want to use it as root, but I don't know what's there - *poof*" and it panics.
>
> If rootwait alone doesn't work, I wonder if root=uuid=2ba08fbc-4b95-46cc-b638-299f16462620 instead of root=/dev/sda2 will work along with rootwait. It should then wait for that fs uuid to become available, rather than waiting for sda2 to become available.
>
> I vaguely recall there recently being btrfs boot problems with the module compiled in…
>

Yes, it was with the crc code.  I noticed he has compression on and I'm 
wondering if we're hitting a similar ordering problem with the zlib init.

The best way to know for sure is to please try with an initrd.  If that 
does work we'll know it's an init ordering problem and we can track it 
down from there.

-chris