On 02/07/2017 12:43 PM, Michal Hocko wrote:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3b93879990fd..7af165d308c4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2342,7 +2342,14 @@ void drain_local_pages(struct zone *zone)
static void drain_local_pages_wq(struct work_struct *work)
{
+ /*
+ * Ordinarily a drain operation is bound to a CPU but may be unbound
+ * after a CPU hotplug operation so it's necessary to disable
+ * preemption for the drain to stabilise the CPU ID.
+ */
+ preempt_disable();
drain_local_pages(NULL);
+ preempt_enable_no_resched();
}
/*
[...]
@@ -6711,7 +6714,16 @@ static int page_alloc_cpu_dead(unsigned int cpu)
{
lru_add_drain_cpu(cpu);
+
+ /*
+ * A per-cpu drain via a workqueue from drain_all_pages can be
+ * rescheduled onto an unrelated CPU. That allows the hotplug
+ * operation and the drain to potentially race on the same
+ * CPU. Serialise hotplug versus drain using pcpu_drain_mutex
+ */
+ mutex_lock(&pcpu_drain_mutex);
drain_pages(cpu);
+ mutex_unlock(&pcpu_drain_mutex);
You cannot put sleepable lock inside the preempt disbaled section...
We can make it a spinlock right?
Could we do flush_work() with a spinlock? Sounds bad too.
Maybe we could just use the fact that the whole drain happens with disabled
irq's and obtain the current cpu under that protection?
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