RT-3.10.6_p3 fails to boot: home.mount mounting timed out

RT-3.10.6_p3 fails to boot: home.mount mounting timed out

[Light]

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  I am trying to build a RT kernel, however it cannot boot because it 
cannot mount /home, which is a subvolume of btrfs.  This is the entry of 
it in /etc/fstab:

/dev/sda3    /home    btrfs 
subvol=gentoohome,defaults,compress=lzo,autodefrag 0 2

I copyed my .config from a working mainline 3.10 kernel(which is able to 
boot) and used "make oldconfig". The resulting config file is almost the 
same with mainline one: I only changed IO scheduler from BFQ(from gentoo 
patchset) to deadline, without even enabling CONFIG_PREEMPT_RT. However 
the RT kernel just cannot boot.

  Could someone help me figure it out? I bought a new recording device 
and need low latency audio system. Thanks!

The attached file includes .config for RT kernel and the working 
mainline kernel, and the boot log of one failed boot.

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Re: RT-3.10.6_p3 fails to boot: home.mount mounting timed out

[Sebastian Andrzej Siewior]

* Light | 2013-10-26 12:35:54 [+0800]:

> I am trying to build a RT kernel, however it cannot boot because it
>cannot mount /home, which is a subvolume of btrfs.  This is the entry
>of it in /etc/fstab:
>
>/dev/sda3    /home    btrfs
>subvol=gentoohome,defaults,compress=lzo,autodefrag 0 2

And this is okay it seems :)

>I copyed my .config from a working mainline 3.10 kernel(which is able
>to boot) and used "make oldconfig". The resulting config file is
>almost the same with mainline one: I only changed IO scheduler from
>BFQ(from gentoo patchset) to deadline, without even enabling
>CONFIG_PREEMPT_RT. However the RT kernel just cannot boot.

That is interresting. Does vanila v3.10.4 / v3.10.6 work? In your
bootlog I see
| Oct 26 11:33:19 Light kernel: 1;39mKernel command line: root=/dev/sda3 rootflags=subvol=gentoo init=/usr/lib/systemd/systemd ro
| Oct 26 11:33:19 Light kernel:  sda: sda1 sda2 sda3 sda4
| Oct 26 11:33:19 Light kernel: VFS: Mounted root (btrfs filesystem) readonly on device 0:12.

which means the disk there and btrfs was able to mount the root
subvolume. However your home subvolume timed out. If there is nothing
different with the way you create the kernel (initramfs and such) then I
have no clue. 
Maybe you could remove /home from fstab and mount it from commandline
because this might show you the error here.

Sebastian

Re: RT-3.10.6_p3 fails to boot: home.mount mounting timed out

[Sebastian Andrzej Siewior]

* Sebastian Andrzej Siewior | 2013-11-22 16:13:44 [+0100]:

>* Light | 2013-10-26 12:35:54 [+0800]:
>
>> I am trying to build a RT kernel, however it cannot boot because it
>>cannot mount /home, which is a subvolume of btrfs.  This is the entry
>>of it in /etc/fstab:
>>
>>/dev/sda3    /home    btrfs
>>subvol=gentoohome,defaults,compress=lzo,autodefrag 0 2

So I tried this myself. I've setup a FC19 box with btrfs with a root
subvolume and a home subvolume. The etc/fstab
|[root@fc19-64 ~]# grep btrfs /etc/fstab 
|UUID=b5045733-8f7d-48e4-a4ad-a58bf44cb49f /      btrfs subvol=root     1 1
|UUID=b5045733-8f7d-48e4-a4ad-a58bf44cb49f /home  btrfs subvol=home     1 1

and it booted:
|[root@fc19-64 ~]# uname -a
|Linux fc19-64.testing 3.12.8-rt10 #250 SMP PREEMPT RT Fri Jan 24 19:18:38 CET 2014 x86_64 x86_64 x86_64 GNU/Linux
|[root@fc19-64 ~]# mount | grep btrfs
|/dev/vda2 on / type btrfs (rw,relatime,seclabel,space_cache)
|/dev/vda2 on /home type btrfs (rw,relatime,seclabel,space_cache)

except for the different mount opts (compress=lzo,autodefrag) I don't
see what is different here.

Sebastian