linux-kernel - Re: [PATCH] mm/page_alloc: deferred meminit: replace rwsem with completion

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Date:	Mon, 6 Jul 2015 09:21:43 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Nicolai Stange <nicstange@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>,
	Alexander Duyck <alexander.h.duyck@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: deferred meminit: replace rwsem with
 completion

On Mon, Jul 06, 2015 at 02:17:30AM +0200, Nicolai Stange wrote:
> Commit 0e1cc95b4cc7
>   ("mm: meminit: finish initialisation of struct pages before basic setup")
> introduced a rwsem to signal completion of the initialization workers.
> 
> Lockdep complains about possible recursive locking:
>   =============================================
>   [ INFO: possible recursive locking detected ]
>   4.1.0-12802-g1dc51b8 #3 Not tainted
>   ---------------------------------------------
>   swapper/0/1 is trying to acquire lock:
>   (pgdat_init_rwsem){++++.+},
>     at: [<ffffffff8424c7fb>] page_alloc_init_late+0xc7/0xe6
> 
>   but task is already holding lock:
>   (pgdat_init_rwsem){++++.+},
>     at: [<ffffffff8424c772>] page_alloc_init_late+0x3e/0xe6
> 
> Replace the rwsem by a completion together with an atomic
> "outstanding work counter".
> 
> Signed-off-by: Nicolai Stange <nicstange@...il.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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