From 1ad0f0a7aa1bf3bd42dcd108a96713d255eacd9f Mon Sep 17 00:00:00 2001
From: Michael Bringmann <mwb@linux.vnet.ibm.com>
Date: Thu, 27 Jul 2017 16:27:14 -0500
Subject: [PATCH] workqueue: Work around edge cases for calc of pool's cpumask
References: bsc#1087405
Patch-mainline: v4.13-rc4
Git-commit: 1ad0f0a7aa1bf3bd42dcd108a96713d255eacd9f
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>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
kernel/workqueue.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 7146ea70a62d..ca937b0c3a96 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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:
--
2.13.6