workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup
commit d6e022f1d207a161cd88e08ef0371554680ffc46 upstream. 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 before874bbfe600
("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. While874bbfe600
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> 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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -568,6 +568,16 @@ static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
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int node)
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{
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assert_rcu_or_wq_mutex_or_pool_mutex(wq);
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/*
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* XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
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* delayed item is pending. The plan is to keep CPU -> NODE
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* mapping valid and stable across CPU on/offlines. Once that
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* happens, this workaround can be removed.
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*/
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if (unlikely(node == NUMA_NO_NODE))
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return wq->dfl_pwq;
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return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
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}
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