linux-kernel - Re: [PATCH 2/9] mm: khugepaged: fix radix tree node leak in shmem collapse error path

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Message-ID: <20161118073029.GB18676@quack2.suse.cz>
Date:   Fri, 18 Nov 2016 08:30:29 +0100
From:   Jan Kara <jack@...e.cz>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 2/9] mm: khugepaged: fix radix tree node leak in shmem
 collapse error path

On Thu 17-11-16 14:11:31, Johannes Weiner wrote:
> The radix tree counts valid entries in each tree node. Entries stored
> in the tree cannot be removed by simpling storing NULL in the slot or
> the internal counters will be off and the node never gets freed again.
> 
> When collapsing a shmem page fails, restore the holes that were filled
> with radix_tree_insert() with a proper radix tree deletion.
> 
> Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
> Reported-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  mm/khugepaged.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index bdfdab40a813..d553c294de40 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1523,9 +1523,11 @@ static void collapse_shmem(struct mm_struct *mm,
>  			if (!page || iter.index < page->index) {
>  				if (!nr_none)
>  					break;
> -				/* Put holes back where they were */
> -				radix_tree_replace_slot(slot, NULL);
>  				nr_none--;
> +				/* Put holes back where they were */
> +				radix_tree_delete(&mapping->page_tree,
> +						  iter.index);
> +				slot = radix_tree_iter_next(&iter);
>  				continue;
>  			}
>  
> -- 
> 2.10.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR