| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 275/342] workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup | Date | Tue, 01 Mar 2016 23:55:31 +0000 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo <tj@kernel.org>
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 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> 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>
--- kernel/workqueue.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -568,6 +568,16 @@ static struct pool_workqueue *unbound_pw 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]); }
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