linux-kernel - Re: [PATCH 1/3] mm, meminit: replace rwsem with completion

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Date:	Fri, 17 Jul 2015 15:12:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nicolai Stange <nicstange@...il.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Alex Ng <alexng@...rosoft.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm, meminit: replace rwsem with completion

On Fri, Jul 17, 2015 at 01:22:02PM +0100, Mel Gorman wrote:
> From: Nicolai Stange <nicstange@...il.com>
> 
> 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".
> 
> [peterz@...radead.org: Barrier removal on the grounds of being pointless]
> [mgorman@...e.de: Applied review feedback]
> Signed-off-by: Nicolai Stange <nicstange@...il.com>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Thanks!
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