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

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Date:   Wed, 19 Apr 2017 16:26:10 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>
Subject: Re: Re: Re: "mm: move pcp and lru-pcp draining into single wq" broke resume
 from s2ram

> 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?