[Bug 1858046] [NEW] qemu-aarch64 hangs on cptofs during a build of NixOS SD card image

From: Ryan Lahfa <1858046@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1858046] [NEW] qemu-aarch64 hangs on cptofs during a build of NixOS SD card image
Date: Wed, 01 Jan 2020 22:15:59 -0000	[thread overview]
Message-ID: <157791695959.3198.15546015289430538780.malonedeb@soybean.canonical.com> (raw)

Public bug reported:

First, thank you for this incredible project.

While following this guide to build my own image of NixOS:
https://nixos.wiki/wiki/NixOS_on_ARM#Compiling_through_QEMU on ARM
Aarch64.

I encountered a very strange behavior, qemu is correctly used and build
most of the binaries until it executes this exact line over qemu:
https://github.com/NixOS/nixpkgs/blob/master/nixos/lib/make-
ext4-fs.nix#L55

At this step, the qemu process goes to 100 % of CPU, hangs in a certain
syscall I don't know which one (according to strace & gdb which has no
symbols so breaking and looking the backtrace was useless).

According to iotop, no I/O was done.

And it spent all its time in this syscall during more than 10 hours,
which looks anomalous to me.

I attach some of my CPU info:

model		: 142
model name	: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
stepping	: 10
microcode	: 0x96
cpu MHz		: 3107.071
cache size	: 8192 KB

I'm using a ThinkPad T480 to perform those builds, I'm uncertain of how
to debug further this issue, I discussed this with some people over
#nixos-aarch64 and they told me they didn't know how to debug it further
too.

I tried all with this package: https://aur.archlinux.org/packages/qemu-
arm-static/ — I'm currently compiling qemu-git to see if it happens on
upstream too. Will comment when it's done.

Thank you in advance!

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1858046

Title:
  qemu-aarch64 hangs on cptofs during a build of NixOS SD card image

Status in QEMU:
  New

Bug description:
  First, thank you for this incredible project.

  While following this guide to build my own image of NixOS:
  https://nixos.wiki/wiki/NixOS_on_ARM#Compiling_through_QEMU on ARM
  Aarch64.

  I encountered a very strange behavior, qemu is correctly used and
  build most of the binaries until it executes this exact line over
  qemu: https://github.com/NixOS/nixpkgs/blob/master/nixos/lib/make-
  ext4-fs.nix#L55

  At this step, the qemu process goes to 100 % of CPU, hangs in a
  certain syscall I don't know which one (according to strace & gdb
  which has no symbols so breaking and looking the backtrace was
  useless).

  According to iotop, no I/O was done.

  And it spent all its time in this syscall during more than 10 hours,
  which looks anomalous to me.

  I attach some of my CPU info:

  model		: 142
  model name	: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
  stepping	: 10
  microcode	: 0x96
  cpu MHz		: 3107.071
  cache size	: 8192 KB

  I'm using a ThinkPad T480 to perform those builds, I'm uncertain of
  how to debug further this issue, I discussed this with some people
  over #nixos-aarch64 and they told me they didn't know how to debug it
  further too.

  I tried all with this package: https://aur.archlinux.org/packages
  /qemu-arm-static/ — I'm currently compiling qemu-git to see if it
  happens on upstream too. Will comment when it's done.

  Thank you in advance!

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