From b1302157d290cf2ed27d3c8ec8414a0b87a16afc Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 3 Feb 2016 13:54:25 -0500 Subject: [PATCH] workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup Orabug: 23330855 [ Upstream commit d6e022f1d207a161cd88e08ef0371554680ffc46 ] 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 Reported-by: Mike Galbraith Cc: Tang Chen Cc: Rafael J. Wysocki Cc: Len Brown 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 Signed-off-by: Sasha Levin Signed-off-by: Dan Duval (cherry picked from f3d69fd89df665c1fa1931f4af846039a4ac5dc4) Conflict: kernel/workqueue.c --- kernel/workqueue.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 5c01664c26e2..5e5cbd834fb7 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -560,7 +560,17 @@ static int worker_pool_assign_id(struct worker_pool *pool) static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq, int node) { - assert_rcu_or_wq_mutex(wq); + 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]); } -- 2.50.1