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[Magali Lemes do Sacramento <2044334@xxxxxxxxxxxxxxxxxx>]

Similar behavior with c4.large instances.
In the 2025.07.14 cycle, we have cpuhotplug:cpuhotplug0{2..6} consistently failing when running with plucky:aws version 6.14.0-1011.11 in the us-west-1 region.
I'd expect the same to be happening with noble:aws-6.14 in this cycle, as these kernels are essentially very similar, but the tests are passing there. However, for n:aws-6.14, they are running in the us-east-2 region.
In the 2025.06.16 cycle, cpuhotplug:cpuhotplug0{2..6} on c4.large running plucky:aws version 6.14.0-1009.9 passed, but they ran in the us-east-2 region too.

I'm thinking if this could have something to do with the region these
instances are launched in. Additionally, x1e.xlarge and c4.large are
both Xen-based, so could this be some intermittent hypervisor issue?

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https://bugs.launchpad.net/bugs/2044334

Title:
  Unable to put CPU back online on AWS x1e.xlarge instance with kernel
  6.2+

Status in ubuntu-kernel-tests:
  New
Status in linux-aws package in Ubuntu:
  New

Bug description:
  Issue found on AWS x1e.xlarge instance with:
  * M-aws 6.5.0-1011.11
  * L-aws 6.2.0-1007.7 
  * J-aws-6.5.0-1008.8~22.04.1
  * J-aws-6.2.0-1005.5~22.04.1 

  J-aws-5.15 looks OK. And I can't see this failure on other instances
  in our pool.

  CPU can be offlined but you won't be able to put it back online.

  There are 4 CPUs on this instance.
  $ uname -a
  Linux ip-172-31-2-102 6.5.0-1011-aws #11~22.04.1-Ubuntu SMP Mon Nov 20 18:38:58 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
  $ grep CONFIG_HOTPLUG_CPU /boot/config-6.5.0-1011-aws 
  CONFIG_HOTPLUG_CPU=y
  $ cat /sys/devices/system/cpu/cpu3/online
  1
  $ echo 0| sudo tee /sys/devices/system/cpu/cpu3/online
  0
  $ echo 1| sudo tee /sys/devices/system/cpu/cpu3/online
  1
  tee: /sys/devices/system/cpu/cpu3/online: Input/output error

  Output from 
  # Offline cpu3 - OK
  Nov 23 06:21:06 ip-172-31-2-102 kernel: [ 1124.449748] smpboot: CPU 3 is now offline
  # Online cpu3 - Failed
  Nov 23 06:21:14 ip-172-31-2-102 kernel: [ 1132.310197] installing Xen timer for CPU 3
  Nov 23 06:21:14 ip-172-31-2-102 kernel: [ 1132.310424] smpboot: Booting Node 0 Processor 3 APIC 0x3
  Nov 23 06:21:24 ip-172-31-2-102 kernel: [ 1142.312481] CPU3 failed to report alive state

  This is affecting the ubuntu_kernel_selftests/cpu-hotplug:cpu-on-off-
  test.sh and ubuntu_ltp/cpuhotplug:cpuhotplug02, cpuhotplug03,
  cpuhotplug04, cpuhotplug06

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