There is an underlying assumption/trade-off in many layers of the Linux
system that CPU <-> node mapping is static. This is despite the presence
of features like NUMA and 'hotplug' that support the dynamic addition/
removal of fundamental system resources like CPUs and memory. PowerPC
systems, however, do provide extensive features for the dynamic change
of resources available to a system.
Currently, there is little or no synchronization protection around the
updating of the CPU <-> node mapping, and the export/update of this
information for other layers / modules. In systems which can change
this mapping during 'hotplug', like PowerPC, the information is changing
underneath all layers that might reference it.
This patch attempts to ensure that a valid, usable cpumask attribute
is used by the workqueue infrastructure when setting up new resource
pools. It prevents a crash that has been observed when an 'empty'
cpumask is passed along to the worker/task scheduling code. It is
intended as a temporary workaround until a more fundamental review and
correction of the issue can be done.
[With additions to the patch provided by Tejun Hao <tj@kernel.org>]
Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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