Commit 1ad0f0a7 authored Jul 27, 2017 by Michael Bringmann Committed by Tejun Heo Jul 28, 2017

workqueue: Work around edge cases for calc of pool's cpumask



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>

parent 0a94efb5

kernel/workqueue.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -3577,6 +3577,13 @@ static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,

		/* yeap, return possible CPUs in @node that @attrs wants */
		cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);

		if (cpumask_empty(cpumask)) {
		pr_warn_once("WARNING: workqueue cpumask: online intersect > "
		"possible intersect\n");
		return false;
		}

		return !cpumask_equal(cpumask, attrs->cpumask);

		use_dfl: