snap refresh hangs on arm architecture

[Ling Gao]

I am a snap developer. And we are testing our snap now the found that snap refresh does not work on a Raspberry Pi 2 and 3. It works on an x86 machines though. Here is the detail:
 I ran "snap refresh --devmode --edge mysnapname" on my rpi2 to pick up the latest snap. It downloaded the new snap, and sometime after displaying [|] Mount snap "mysnapname" (53) it threw me into kdb on the console. After rebooting, the new snap seems to be working ok. The same thing happen on rpi3.
Image:
pi2:
    IMAGE="ubuntu-16.04-preinstalled-server-armhf+raspi2.img"
    URL="http://cdimage.ubuntu.com/ubuntu/releases/16.04/release/$IMAGE.xz"
pi3:
    IMAGE="ubuntu-16.04-preinstalled-server-armhf+raspi3.img"
    URL="http://www.finnie.org/software/raspberrypi/ubuntu-rpi3/$IMAGE.xz"

Kernel debugging session output for rpi3:
[336032.404195] Unable to handle kernel NULL pointer dereference at virtual address 00000008
[336032.417227] pgd = b66fc000
[336032.422448] [00000008] *pgd=21359831, *pte=00000000, *ppte=00000000
[336032.432174] Internal error: Oops: 17 [#1] SMP ARM

Entering kdb (current=0xa11aca40, pid 7068) on processor 0 Oops: (null)
due to oops @ 0x802dad7c
CPU: 0 PID: 7068 Comm: mount Not tainted 4.4.0-1009-raspi2 #10-Ubuntu
Hardware name: BCM2709
task: a11aca40 ti: a7d5e000 task.ti: a7d5e000
PC is at propagate_one+0xc4/0x1b0
LR is at 0xb8be6f00
pc : [<802dad7c>] lr : [] psr: 800d0013
sp : a7d5fe40 ip : 000000de fp : a7d5fe5c
r10: 00000000 r9 : a1245cc0 r8 : b8f2f300
r7 : a7d5fe88 r6 : 00000000 r5 : b8f2f300 r4 : 81041f98
r3 : 00000001 r2 : 00000000 r1 : b8f2f540 r0 : 00000000
Flags: Nzcv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
Control: 10c5383d Table: 366fc06a DAC: 00000055
CPU: 0 PID: 7068 Comm: mount Not tainted 4.4.0-1009-raspi2 #10-Ubuntu
Hardware name: BCM2709
[<80111f34>] (unwind_backtrace) from [<8010d198>] (show_stack+0x20/0x24)
[<8010d198>] (show_stack) from [<8055412c>] (dump_stack+0xc8/0x10c)
[<8055412c>] (dump_stack) from [<80109b3c>] (show_regs+0x1c/0x20)
[<80109b3c>] (show_regs) from [<801e36b0>] (kdb_main_loop+0x348/0x7b0)
[<801e36b0>] (kdb_main_loop) from [<801e6818>] (kdb_stub+0x2d0/0x528)
[<801e6818>] (kdb_stub) from [<801dbd30>] (kgdb_cpu_enter+0x460/0x7f0)
[<801dbd30>] (kgdb_cpu_enter) from [<801dc33c>] (kgdb_handle_exception+0x124/0x234)
[<801dc33c>] (kgdb_handle_exception) from [<80111234>] (kgdb_notify+0x40/0x90)
[<80111234>] (kgdb_notify) from [<80146528>] (notifier_call_chain+0x54/0x94)
[<80146528>] (notifier_call_chain) from [<801467d0>] (notify_die+0x58/0x78)
[<801467d0>] (notify_die) from [<8010d2c8>] (die+0x12c/0x498)
[<8010d2c8>] (die) from [<8011b520>] (__do_kernel_fault.part.0+0x74/0x1f4)
[<8011b520>] (__do_kernel_fault.part.0) from [<809ce190>] (do_page_fault+0x23c/0x3b8)
[<809ce190>] (do_page_fault) from [<80101230>] (do_DataAbort+0x58/0xe8)
[<80101230>] (do_DataAbort) from [<809cd7dc>] (__dabt_svc+0x3c/0x60)
Exception stack(0xa7d5fdf0 to 0xa7d5fe38)
fde0: 00000000 b8f2f540 00000000 00000001
fe00: 81041f98 b8f2f300 00000000 a7d5fe88 b8f2f300 a1245cc0 00000000 a7d5fe5c
fe20: 000000de a7d5fe40 b8be6f00 802dad7c 800d0013 ffffffff
[<809cd7dc>] (__dabt_svc) from [<802dad7c>] (propagate_one+0xc4/0x1b0)
[<802dad7c>] (propagate_one) from [<802db22c>] (propagate_mnt+0x128/0x154)
[<802db22c>] (propagate_mnt) from [<802cacb8>] (attach_recursive_mnt+0x16c/0x284)
[<802cacb8>] (attach_recursive_mnt) from [<802cae3c>] (graft_tree+0x6c/0x9c)
[<802cae3c>] (graft_tree) from [<802caf08>] (do_add_mount+0x9c/0xf0)
[<802caf08>] (do_add_mount) from [<802cbef4>] (do_mount+0x284/0xd70)
[<802cbef4>] (do_mount) from [<802ccdcc>] (SyS_mount+0xb4/0xf4)
[<802ccdcc>] (SyS_mount) from [<80108d00>] (ret_fast_syscall+0x0/0x1c)

[Paolo Pisati (p-pisati)]

Kernel version?

Please use the rpi2 16.04 image you linked above, dist-upgrade it to the latest kernel, reboot, retry and report.

[Ling Gao (linggao)]

Kernel version is: 4.4.0-1009-raspi2
Linux version 4.4.0-1009-raspi2 (buildd@kishi11) (gcc version 5.3.1 20160413 (Ubuntu/Linaro 5.3.1-14ubuntu2) ) #10-Ubuntu SMP Tue Apr 19 19:51:04 UTC 2016

[Ling Gao (linggao)]

I ran the following commands to upgrade:
apt-get update
apt-get upgrade
apt-get dist-upgrade
Then rebooted.
snap refresh died when Mounting. Same problem.
Question: is this the right way to upgrade the kernel? What is the version of the latest kernel?

[Loïc Minier (lool)]

This shows RPi kernel for Ubuntu 16.04 versions:
https://launchpad.net/ubuntu/+source/linux-raspi2

Latest in xenial-updates is 4.4.0-1042.49, so you seem to have an older version.

Could you check that you have xenial-updates in your /etc/apt/sources.list*?

What's the reported .deb version with dpkg -l linux-image\*|grep ^ii

If you have the latest deb but not the latest kernel installed, this might indicate a non-working flash-kernel upgrade

[Ling Gao (linggao)]

#cat /etc/apt/sources.list*
deb http://ports.ubuntu.com/ubuntu-ports/ xenial main restricted universe multiverse
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main restricted universe multiverse
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-security main restricted universe multiverse

# dpkg -l linux-image\*|grep ^ii
ii linux-image-4.4.0-1009-raspi2 4.4.0-1009.10 armhf Linux kernel image for version 4.4.0 on ARM (hard float) SMP

[Ling Gao (linggao)]

# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  linux-firmware linux-firmware-raspi2 linux-headers-raspi2 linux-image-raspi2 linux-raspi2
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.

[Ling Gao (linggao)]

# apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  linux-firmware linux-firmware-raspi2 linux-headers-raspi2 linux-image-raspi2 linux-raspi2
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.

[Ling Gao (linggao)]

I got the rpi2 upgraded to the latest kernel version 4.4.0-1042-raspi2, rebooted the it and the snap refresh works now.
Here is what I did to upgrade the kernel.
apt-get update
apt-get upgrade
apt-get dist-upgrade
apt-get upgrade linux-firmware linux-firmware-raspi2 linux-headers-raspi2 linux-image-raspi2 linux-raspi2

I will take a look at our rpi2 and 3 image build process to see how to get the kernel updated in the image.
Thanks for all the help.

[Ling Gao (linggao)]

We have built new images for pi2 and pi3 with the latest kernel (version 4.4.0-1042-raspi2 or 3) and the snap refresh works now. Thanks for the help. This bug can be closed now. Thanks again.