Messages in this thread | | | Date | Tue, 7 Feb 2017 13:03:50 +0000 | From | Mel Gorman <> | Subject | Re: mm: deadlock between get_online_cpus/pcpu_alloc |
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On Tue, Feb 07, 2017 at 12:43:27PM +0100, Michal Hocko wrote: > > Right. The unbind operation can set a mask that is any allowable CPU and > > the final process_work is not done in a context that prevents > > preemption. > > > > 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? >
The CPU down callback can hold a mutex and at least he SLUB callback already does so. That gives
page_alloc_cpu_dead mutex_lock drain_pages mutex_unlock
drain_all_pages mutex_lock queue workqueue drain_local_pages_wq preempt_disable drain_local_pages drain_pages preempt_enable flush queues mutex_unlock
I must be blind or maybe it's rushing between multiple concerns but which sleepable lock is of concern?
-- Mel Gorman SUSE Labs
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