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[Thadeu Lima de Souza Cascardo <1866149@xxxxxxxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu)
       Status: Incomplete => Invalid

** Changed in: linux (Ubuntu Xenial)
       Status: New => Invalid

** Changed in: linux (Ubuntu Bionic)
       Status: New => Invalid

** Changed in: linux (Ubuntu Focal)
       Status: New => Invalid

** Changed in: linux (Ubuntu Groovy)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1866149

Title:
  CONFIG_BASE_SMALL=1 restricts pid space, which conflicts with systemd
  default sysctl

Status in linux package in Ubuntu:
  Invalid
Status in linux-kvm package in Ubuntu:
  Incomplete
Status in linux source package in Xenial:
  Invalid
Status in linux-kvm source package in Xenial:
  In Progress
Status in linux source package in Bionic:
  Invalid
Status in linux-kvm source package in Bionic:
  In Progress
Status in linux source package in Focal:
  Invalid
Status in linux-kvm source package in Focal:
  In Progress
Status in linux source package in Groovy:
  Invalid
Status in linux-kvm source package in Groovy:
  In Progress

Bug description:
  [Impact]
  systemd-systemctl will fail to set kernel.pid_max, leading to a degraded boot.

  [Fix]
  Set CONFIG_BASE_FULL=y, CONFIG_BASE_SMALL=0.

  [Test case]
  Write 419304 to /proc/sys/kernel/pid_max.

  [Potential regression]
  Boot time may be affected.

  
  ====================================================================

  I'm not completely sure which package to log this against.

  I'm running the kvm focal minimal cloud image from 20200302. I noticed
  on boot that there was an error complaining that systemd-systemctl
  couldn't update pid_max to the value it wanted:

  systemd-sysctl[117]: Couldn't write '4194304' to 'kernel/pid_max':
  Invalid argument

  Digging into it a bit more, this comes from /usr/lib/sysctl.d/50-pid-max.conf:
  # Bump the numeric PID range to its maximum of 2^22 (from the in-kernel default
  # of 2^16), to make PID collisions less likely.
  kernel.pid_max = 4194304

  However, the linux-image-kvm kernel is compiled with
  CONFIG_BASE_SMALL=1

  and this triggers the following code in include/linux/threads.h

  #define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \
   (sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))

  which means that if CONFIG_BASE_SMALL is set we get a maximum limit of
  PAGE_SIZE * 8, which on x86 would be 32768.

  As a workaround I can override it with a file in /etc/sysctl.d/ but
  this shouldn't be needed.

  I really don't know if CONFIG_BASE_SMALL makes any sense on x86 cloud
  images, they really aren't small machines in the scheme of things!

  Cheers

  David

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