[Bug 1861161] Re: qemu-arm-static stuck with 100% CPU when cross-compiling emacs

[Philippe Vaucher]

I tried several workarounds including removing `dir_index` from ext4
partitions and using a 32 bit qemu-user-static version, but it does not
work:

The process still gets stuck in a loop involving `getdents64`:


```
root@earth:~# file /usr/bin/qemu-arm-static
/usr/bin/qemu-arm-static: ELF 32-bit LSB executable, Intel 80386, version 1 
(GNU/Linux), statically linked, for GNU/Linux 3.2.0, 
BuildID[sha1]=ff1224d87ca5dece8d0b0f5735cfee7fae97ee58, stripped

root@earth:~# ps afx | grep qemu
21031 pts/0    S+     0:00          \_ grep --color=auto qemu
 1036 ?        Ss     0:00 /usr/sbin/qemu-ga --daemonize -m virtio-serial -p 
/dev/virtio-ports/org.qemu.guest_agent.0
10584 ?        Ssl    0:00      |   |   \_ /usr/bin/qemu-arm-static 
/usr/bin/make install
28768 ?        Sl     0:01      |   |       \_ /usr/bin/qemu-arm-static 
/usr/bin/make -C src VCSWITNESS=$(srcdir)/../.git/logs/HEAD all
16718 ?        Sl     0:00      |   |           \_ /usr/bin/qemu-arm-static 
/usr/bin/make -C ../lisp compile-first EMACS=../src/bootstrap-emacs
16726 ?        Rl    48:24      |   |               \_ /usr/bin/qemu-arm-static 
../src/bootstrap-emacs -batch --no-site-file --no-site-lisp --eval (setq 
load-prefer-newer t) -f batch-byte-compile emacs-lisp/macroexp.el
10696 ?        Ssl    0:00      |       \_ /usr/bin/qemu-aarch64-static 
/usr/bin/make install
10972 ?        Sl     0:02      |           \_ /usr/bin/qemu-aarch64-static 
/usr/bin/make -C src VCSWITNESS=$(srcdir)/../.git/logs/HEAD all
20397 ?        Sl     0:00      |               \_ /usr/bin/qemu-aarch64-static 
/usr/bin/make -C ../lisp compile-first EMACS=../src/bootstrap-emacs
20405 ?        Rl    24:09      |                   \_ 
/usr/bin/qemu-aarch64-static ../src/bootstrap-emacs -batch --no-site-file 
--no-site-lisp --eval (setq load-prefer-newer t) -f batch-byte-compile 
emacs-lisp/macroexp.el

root@earth:~# strace -p 16726
clock_gettime(CLOCK_REALTIME, {tv_sec=1584794027, tv_nsec=921230669}) = 0
getdents64(5, /* 0 entries */, 2048)    = 0
_llseek(5, 0, [0], SEEK_SET)            = 0
getdents64(5, /* 5 entries */, 2048)    = 144
tgkill(29984, 29987, SIGRT_2)           = -1 EAGAIN (Resource temporarily 
unavailable)
clock_gettime(CLOCK_REALTIME, {tv_sec=1584794027, tv_nsec=921642405}) = 0
getdents64(5, /* 0 entries */, 2048)    = 0
_llseek(5, 0, [0], SEEK_SET)            = 0
getdents64(5, /* 5 entries */, 2048)    = 144
tgkill(29984, 29987, SIGRT_2)           = -1 EAGAIN (Resource temporarily 
unavailable)
clock_gettime(CLOCK_REALTIME, {tv_sec=1584794027, tv_nsec=922333065}) = 0
getdents64(5, /* 0 entries */, 2048)    = 0
_llseek(5, 0, [0], SEEK_SET)            = 0
getdents64(5, /* 5 entries */, 2048)    = 144
tgkill(29984, 29987, SIGRT_2)           = -1 EAGAIN (Resource temporarily 
unavailable)
clock_gettime(CLOCK_REALTIME, ^C{tv_sec=1584794027, tv_nsec=923201432}) = 0
strace: Process 16726 detached
```

What is interesting is that the qemu-aarch64-static process also get
stuck, which if I understand the bug correctly should not happen. I'll
try stracing the process to figure out what happens.

-- 
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https://bugs.launchpad.net/bugs/1861161

Title:
  qemu-arm-static stuck with 100% CPU when cross-compiling emacs

Status in QEMU:
  New

Bug description:
  Hello,

  I'm trying to build multi-arch docker images for
  https://hub.docker.com/r/silex/emacs.

  Here is the machine I'm building on (hetzner cloud machine):

  root@ubuntu-4gb-fsn1-1:~# lsb_release -a
  No LSB modules are available.
  Distributor ID: Ubuntu
  Description:    Ubuntu 18.04.3 LTS
  Release:        18.04
  Codename:       bionic
  root@ubuntu-4gb-fsn1-1:~# uname -a
  Linux ubuntu-4gb-fsn1-1 4.15.0-74-generic #84-Ubuntu SMP Thu Dec 19 08:06:28 
UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

  Whenever I try to build the following alpine Dockerfile
  https://gitlab.com/Silex777/docker-
  emacs/blob/master/26.3/alpine/3.9/dev/Dockerfile like this:

  $ sysctl kernel.randomize_va_space=0
  $ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
  $ docker build --pull -t test --platform arm .

  It builds fine until this:

  root@ubuntu-4gb-fsn1-1:~# ps -ef | grep qemu
  root     26473 26465 99 14:26 pts/0    01:59:58 /usr/bin/qemu-arm-static 
../src/bootstrap-emacs -batch --no-site-file --no-site-lisp --eval (setq 
load-prefer-newer t) -f batch-byte-compile emacs-lisp/macroexp.el

  This is supposed to take a few seconds, but here it takes 100% CPU and
  never ends. When I strace the process I see a never ending loop like
  this:

  getdents64(5, /* 0 entries */, 2048)    = 0
  lseek(5, 0, SEEK_SET)                   = 0
  getdents64(5, /* 5 entries */, 2048)    = 120
  tgkill(5875, 5878, SIGRT_2)             = -1 EAGAIN (Resource temporarily 
unavailable)
  getdents64(5, /* 0 entries */, 2048)    = 0
  lseek(5, 0, SEEK_SET)                   = 0
  getdents64(5, /* 5 entries */, 2048)    = 120
  tgkill(5875, 5878, SIGRT_2)             = -1 EAGAIN (Resource temporarily 
unavailable)
  getdents64(5, /* 0 entries */, 2048)    = 0
  lseek(5, 0, SEEK_SET)                   = 0
  getdents64(5, /* 5 entries */, 2048)    = 120
  tgkill(5875, 5878, SIGRT_2)             = -1 EAGAIN (Resource temporarily 
unavailable)
  getdents64(5, /* 0 entries */, 2048)    = 0
  lseek(5, 0, SEEK_SET)                   = 0
  getdents64(5, /* 5 entries */, 2048)    = 120
  tgkill(5875, 5878, SIGRT_2)             = -1 EAGAIN (Resource temporarily 
unavailable)
  getdents64(5, /* 0 entries */, 2048)    = 0
  lseek(5, 0, SEEK_SET)                   = 0
  getdents64(5, /* 5 entries */, 2048)    = 120
  tgkill(5875, 5878, SIGRT_2)             = -1 EAGAIN (Resource temporarily 
unavailable)

  It happens with all the QEMU versions I tested:
  - 2.11.1 (OS version)
  - 4.1.1-1 (from multiarch/qemu-user-static:4.1.1-1)
  - 4.2.0-2 (from multiarch/qemu-user-static)

  Any ideas of what I could do to debug it further?

  Kind regards,
  Philippe

  p.s: Everything builds fine when the base image is ubuntu. I also had
  similar hangs with basic commands like "apt-get install foo"
  sometimes.

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