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Date: Tue, 17 Dec 2013 22:32:53 -0500
From: Sasha Levin <sasha.levin@oracle.com>
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To: Wanpeng Li <liwanp@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>
CC: Michel Lespinasse <walken@google.com>, Bob Liu <bob.liu@oracle.com>,
        npiggin@suse.de, kosaki.motohiro@jp.fujitsu.com, riel@redhat.com,
        David Rientjes <rientjes@google.com>, Mel Gorman <mgorman@suse.de>,
        Minchan Kim <minchan@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
        Hugh Dickins <hughd@google.com>, Johannes Weiner <hannes@cmpxchg.org>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs
References: <1387267550-8689-1-git-send-email-liwanp@linux.vnet.ibm.com> <52b1138b.0201430a.19a8.605dSMTPIN_ADDED_BROKEN@mx.google.com> <20131218032329.GA6044@hacker.(null)>
In-Reply-To: <20131218032329.GA6044@hacker.(null)>
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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