linux-kernel - Re: [PATCH 1/3] mm/mlock.c: convert put_page() to put_user

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Date:   Wed, 7 Aug 2019 13:01:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     john.hubbard@...il.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jerome Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Black <daniel@...ux.ibm.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 1/3] mm/mlock.c: convert put_page() to put_user_page*()

On Mon 05-08-19 15:20:17, john.hubbard@...il.com wrote:
> From: John Hubbard <jhubbard@...dia.com>
> 
> For pages that were retained via get_user_pages*(), release those pages
> via the new put_user_page*() routines, instead of via put_page() or
> release_pages().

Hmm, this is an interesting code path. There seems to be a mix of pages
in the game. We get one page via follow_page_mask but then other pages
in the range are filled by __munlock_pagevec_fill and that does a direct
pte walk. Is using put_user_page correct in this case? Could you explain
why in the changelog?

> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
> ("mm: introduce put_user_page*(), placeholder versions").
> 
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Daniel Black <daniel@...ux.ibm.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>  mm/mlock.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index a90099da4fb4..b980e6270e8a 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -345,7 +345,7 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
>  				get_page(page); /* for putback_lru_page() */
>  				__munlock_isolated_page(page);
>  				unlock_page(page);
> -				put_page(page); /* from follow_page_mask() */
> +				put_user_page(page); /* from follow_page_mask() */
>  			}
>  		}
>  	}
> @@ -467,7 +467,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
>  		if (page && !IS_ERR(page)) {
>  			if (PageTransTail(page)) {
>  				VM_BUG_ON_PAGE(PageMlocked(page), page);
> -				put_page(page); /* follow_page_mask() */
> +				put_user_page(page); /* follow_page_mask() */
>  			} else if (PageTransHuge(page)) {
>  				lock_page(page);
>  				/*
> @@ -478,7 +478,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
>  				 */
>  				page_mask = munlock_vma_page(page);
>  				unlock_page(page);
> -				put_page(page); /* follow_page_mask() */
> +				put_user_page(page); /* follow_page_mask() */
>  			} else {
>  				/*
>  				 * Non-huge pages are handled in batches via
> -- 
> 2.22.0

-- 
Michal Hocko
SUSE Labs