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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

This bug was nominated against a series that is no longer supported, ie
quantal.  The bug task representing the quantal nomination is being
closed as Won't Fix.

This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.

** Changed in: linux (Ubuntu Quantal)
       Status: Fix Committed => Won't Fix

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https://bugs.launchpad.net/bugs/1168452

Title:
  NULL pointer dereference when offlining CPU on DL385p Gen8

Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux” source package in Quantal:
  Won't Fix
Status in “linux” source package in Raring:
  Fix Released

Bug description:
  == Quantal SRU Justification ==
  When we try to offline a CPU on DL385p Gen8 with Abu Dhabi processor then we see a NULL pointer dereference kernel oops:

  https://bugs.launchpad.net/hp/+bug/1132956/+attachment/3546712/+files/kernel_panic.jpg

  The latest Raring kernel works fine on the same system.  Upon
  investigation, we have identified a straightforward fix to check the
  device pointer and thus avoid the NULL pointer dereference.

  == Test Case ==
  With 1P on the same system everything works fine.
  command to offline a cpu is
  echo "0" > /sys/devices/system/cpu/cpu12/online

  == Investigation ==
  There are actually a few commits in Raring which prevent the Oops from occuring.  HP originally pointed us to the following commits to resolve the Oops:

  http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-raring.git;a=commitdiff;h=bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92
  http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-raring.git;a=commitdiff;h=13dd52f11a04e616900f565d6a1e5138e58d579f

  However, when examining the commit bf4d1b5d "cpuidle: support multiple
  drivers", it's clearly aimed at arm platforms...This option is
  configurable at compile time and should be enabled for the tegra3 and
  big.LITTLE architectures.  There is no impact for other platforms if
  the option is disabled.  The option defaults to 'n'.  And indeed in
  Raring, CONFIG_CPU_IDLE_MULTIPLE_DRIVERS is not set for amd64.  So I
  was highly skeptical that this was the proper fix we wanted.  Also, in
  order to cleanly cherry-pick the above into Quantal,  one would have
  to also pick up the following set:

  12c46e70e44728c58f96409414ff06e90e1354f0 [Config] UBUNTU: Enable CONFIG_CPU_IDLE_MULTIPLE_DRIVERS
  bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92 cpuidle: support multiple drivers
  1aef40e288acfb3cc28ff77528b34ef66683bed6 cpuidle / sysfs: change function parameter
  3af272ab75c7a0c7fa5ae5507724d961f7e7718b cpuidle: fix error handling in __cpuidle_register_device
  cf31cd1a0c692a1445c80756055875088fa29982 ACPI idle, CPU hotplug: Fix NULL pointer dereference during hotplug
  1b0a0e9a15b976d91f3b5ae619c6a8964c2818eb cpuidle: add checks to avoid NULL pointer dereference
  0aeb9cac6f8a6fc68acfb07d30b62ad6106a6384 cpuidle: remove unused hrtimer_peek_ahead_timers() call
  13dd52f11a04e616900f565d6a1e5138e58d579f cpuidle: prepare the cpuidle core to handle multiple drivers
  41682032715c2c969357c81391a442a24dd1c2c2 cpuidle: move driver checking within the lock section
  42f67f2acab2b7179c0d1ab234869e391448dfa6 cpuidle: move driver's refcount to cpuidle
  ed953472d181e1d149f17d85d82de9634db296c3 cpuidle: rename function name "__cpuidle_register_driver", v2
  a77de28662adea391d8ed952e2b9c49b60193e8c cpuidle: remove some empty lines
  6e797a078824b30afbfae6cc4b1c2b21c51761ef PM / cpuidle: Add driver reference counter

  Upon further examination of the Oops, I confirmed that the following
  upstream commit would also avoid the issue:

  commit ac3ebafa81af76d65e4fb45c6388f08e90ddcc6d
  Author: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
  Date:   Mon Feb 4 22:44:43 2013 +0000

      ACPI / idle: remove usage of the statedata

  However, this change seems more of a band-aid solution to the root
  cause because it removes all remaining references to state_usage and
  thus avoiding any pointer dereferencing all together, but clearly
  doesn't addressing the fact that the pointer was NULL to begin with.

  Going back to a closer examination of "cpuidle: support multiple
  drivers", even though it claims to have no other impact on other
  platforms if disabled, it clearly makes one change which does affect
  all platforms.  It replaces all calls to cpuidle_get_driver() with a
  new call to cpuidle_get_cpu_driver().  This new call
  cpuidle_get_cpu_driver() adds a check if (!dev) return NULL which then
  propogates back up to eventually return -ENODEV.  It is this
  additional error checking which is missing from the Quantal code base.

  == Fix ==
  Add device error checking to avoid NULL pointer dereference kernel Oops when offlining CPU's (See patch attached to bug report).  We have tested this patch against a DL385p Gen8 and confirm we no longer experience a kernel oops when offlining CPU's.

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