linux-kernel - Re: [PATCH 3/4] mm: gup: use get_user_pages_fast and get_user_pages

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Message-ID: <542C31E0.5040909@oracle.com>
Date:	Wed, 01 Oct 2014 12:54:56 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Andrea Arcangeli <aarcange@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
CC:	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Gleb Natapov <gleb@...nel.org>,
	Radim Krcmar <rkrcmar@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jianyu Zhan <nasa4836@...il.com>,
	Paul Cassella <cassella@...y.com>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Feiner <pfeiner@...gle.com>,
	"Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH 3/4] mm: gup: use get_user_pages_fast and get_user_pages_unlocked

Hi Andrea,

On 10/01/2014 04:56 AM, Andrea Arcangeli wrote:
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 8f5330d..6606c10 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -881,7 +881,7 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr)
>  	struct page *p;
>  	int err;
>  
> -	err = get_user_pages(current, mm, addr & PAGE_MASK, 1, 0, 0, &p, NULL);
> +	err = get_user_pages_fast(addr & PAGE_MASK, 1, 0, &p);
>  	if (err >= 0) {
>  		err = page_to_nid(p);
>  		put_page(p);

This change looks bogus. mmap_sem might get locked in do_get_mempolicy(), and with this
change we'll try locking it again in get_user_pages_fast.


Thanks,
Sasha
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