Re: Re: Re: "mm: move pcp and lru-pcp draining into single wq" broke resume from s2ram

[Michal Hocko]

On Wed 19-04-17 16:26:10, Tetsuo Handa wrote:
> > On Wed 19-04-17 14:41:30, Tetsuo Handa wrote:
> > [...]
> > > Somebody is waiting forever with cpu_hotplug.lock held?
> > 
> > Why would that matter for drain_all_pages? It doesn't use
> > get_online_cpus since a459eeb7b852 ("mm, page_alloc: do not depend on
> > cpu hotplug locks inside the allocator") while ce612879ddc7 ("mm: move
> > pcp and lru-pcp draining into single wq") was merged later.
> > 
> 
> Looking at ce612879ddc7 ("mm: move pcp and lru-pcp draining into single wq"),
> we merged "lru-add-drain" (!WQ_FREEZABLE && WQ_MEM_RECLAIM) workqueue and
> "vmstat" (WQ_FREEZABLE && WQ_MEM_RECLAIM) workqueue into
> "mm_percpu_wq" (WQ_FREEZABLE && WQ_MEM_RECLAIM) workqueue.
> 
> -       lru_add_drain_wq = alloc_workqueue("lru-add-drain", WQ_MEM_RECLAIM, 0);
> -       vmstat_wq = alloc_workqueue("vmstat", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> +       mm_percpu_wq = alloc_workqueue("mm_percpu_wq",
> +                                      WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> 
> That means "lru-add-drain" became freezable, doesn't it? And this problem
> occurs around resume operation where all freezable threads are frozen?
> Then, lru_add_drain_per_cpu() cannot be performed due to mm_percpu_wq frozen?

Ohh, right you are! Very well spotted. I have completely missed
WQ_FREEZABLE there. The following should work
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