CPU hotplug, cpusets, suspend: Don't touch cpusets during suspend/resume
authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Thu, 23 Feb 2012 09:57:15 +0000 (15:27 +0530)
committerIngo Molnar <mingo@elte.hu>
Mon, 27 Feb 2012 10:38:13 +0000 (11:38 +0100)
commit8f2f748b0656257153bcf0941df8d6060acc5ca6
tree960e37a40212b88dd25be216addf7381c87c84fe
parent8c79a045fd590a26e81e75f5d8d4ec5c7d23e565
CPU hotplug, cpusets, suspend: Don't touch cpusets during suspend/resume

Currently, during CPU hotplug, the cpuset callbacks modify the cpusets
to reflect the state of the system, and this handling is asymmetric.
That is, upon CPU offline, that CPU is removed from all cpusets. However
when it comes back online, it is put back only to the root cpuset.

This gives rise to a significant problem during suspend/resume. During
suspend, we offline all non-boot cpus and during resume we online them back.
Which means, after a resume, all cpusets (except the root cpuset) will be
restricted to just one single CPU (the boot cpu). But the whole point of
suspend/resume is to restore the system to a state which is as close as
possible to how it was before suspend.

So to fix this, don't touch cpusets during suspend/resume. That is, modify
the cpuset-related CPU hotplug callback to just ignore CPU hotplug when it
is initiated as part of the suspend/resume sequence.

Reported-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/4F460D7B.1020703@linux.vnet.ibm.com
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kernel/sched/core.c