linux-kernel - Re: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs

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Date:	Tue, 17 Dec 2013 22:32:53 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Michel Lespinasse <walken@...gle.com>,
	Bob Liu <bob.liu@...cle.com>, npiggin@...e.de,
	kosaki.motohiro@...fujitsu.com, riel@...hat.com,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs

On 12/17/2013 10:23 PM, Wanpeng Li wrote:
> -			mlock_vma_page(page);   /* no-op if already mlocked */
> -			if (page == check_page)
> +			if (page != check_page && trylock_page(page)) {
> +				mlock_vma_page(page);   /* no-op if already mlocked */
> +				unlock_page(page);
> +			} else if (page == check_page) {
> +				mlock_vma_page(page);  /* no-op if already mlocked */
>   				ret = SWAP_MLOCK;
> +			}

Previously, if page != check_page and the page was locked, we'd call mlock_vma_page()
anyways. With this change, we don't. In fact, we'll just skip that entire block not doing
anything.

If that's something that's never supposed to happen, can we add a

	VM_BUG_ON(page != check_page && PageLocked(page))

Just to cover this new code path?


Thanks,
Sasha
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