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authorTejun Heo <tj@kernel.org>2016-02-03 13:54:25 -0500
committerTejun Heo <tj@kernel.org>2016-02-10 12:13:05 -0500
commitd6e022f1d207a161cd88e08ef0371554680ffc46 (patch)
tree8c7af29b169c0d0cea4112e6365dae3cff13eda8 /kernel/workqueue.c
parentf303fccb82928790ec58eea82722bd5c54d300b3 (diff)
downloadlinux-sh-d6e022f1d207a161cd88e08ef0371554680ffc46.tar.gz
workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup
When looking up the pool_workqueue to use for an unbound workqueue, workqueue assumes that the target CPU is always bound to a valid NUMA node. However, currently, when a CPU goes offline, the mapping is destroyed and cpu_to_node() returns NUMA_NO_NODE. This has always been broken but hasn't triggered often enough before 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu"). After the commit, workqueue forcifully assigns the local CPU for delayed work items without explicit target CPU to fix a different issue. This widens the window where CPU can go offline while a delayed work item is pending causing delayed work items dispatched with target CPU set to an already offlined CPU. The resulting NUMA_NO_NODE mapping makes workqueue try to queue the work item on a NULL pool_workqueue and thus crash. While 874bbfe600a6 has been reverted for a different reason making the bug less visible again, it can still happen. Fix it by mapping NUMA_NO_NODE to the default pool_workqueue from unbound_pwq_by_node(). This is a temporary workaround. The long term solution is keeping CPU -> NODE mapping stable across CPU off/online cycles which is being worked on. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Tang Chen <tangchen@cn.fujitsu.com> Cc: Rafael J. Wysocki <rafael@kernel.org> Cc: Len Brown <len.brown@intel.com> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/g/1454424264.11183.46.camel@gmail.com Link: http://lkml.kernel.org/g/1453702100-2597-1-git-send-email-tangchen@cn.fujitsu.com
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 51d77e7c0989..7ff5dc7d2ac5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -586,6 +586,16 @@ static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
int node)
{
assert_rcu_or_wq_mutex_or_pool_mutex(wq);
+
+ /*
+ * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
+ * delayed item is pending. The plan is to keep CPU -> NODE
+ * mapping valid and stable across CPU on/offlines. Once that
+ * happens, this workaround can be removed.
+ */
+ if (unlikely(node == NUMA_NO_NODE))
+ return wq->dfl_pwq;
+
return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
}