Public bug reported:

CPU offlining can trigger hangs with HP ProLiant DL360p Gen8 on Ubuntu
17.10.

The hangs also occur with latest mainline kernel Linux 4.15-rc8.

I bisected the upstream mainline kernel. This is a regression introduced
by Linux 4.13-rc1 commit c5cb83bb337c25caae995d992d1cdf9b317f83de
("genirq/cpuhotplug: Handle managed IRQs on CPU hotplug").
https://github.com/torvalds/linux/commit/c5cb83bb337c25caae995d992d1cdf9b317f83de

This test case to offline all CPUs except for CPU 0 can be used to
trigger a hang.

for i in $(seq 1 $(expr $(nproc --all) - 1)); do sudo sh -c "echo 0 >
/sys/devices/system/cpu/cpu$i/online"; done

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete


** Tags: artful bionic

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https://bugs.launchpad.net/bugs/1744163

Title:
  CPU offlining can trigger hangs with HP ProLiant DL360p Gen8.

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  CPU offlining can trigger hangs with HP ProLiant DL360p Gen8 on Ubuntu
  17.10.

  The hangs also occur with latest mainline kernel Linux 4.15-rc8.

  I bisected the upstream mainline kernel. This is a regression
  introduced by Linux 4.13-rc1 commit
  c5cb83bb337c25caae995d992d1cdf9b317f83de ("genirq/cpuhotplug: Handle
  managed IRQs on CPU hotplug").
  
https://github.com/torvalds/linux/commit/c5cb83bb337c25caae995d992d1cdf9b317f83de

  This test case to offline all CPUs except for CPU 0 can be used to
  trigger a hang.

  for i in $(seq 1 $(expr $(nproc --all) - 1)); do sudo sh -c "echo 0 >
  /sys/devices/system/cpu/cpu$i/online"; done

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