Patchwork [2/9] mm: khugepaged: fix radix tree node leak in shmem collapse error path

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Submitter Johannes Weiner
Date Nov. 17, 2016, 7:11 p.m.
Message ID <20161117191138.22769-3-hannes@cmpxchg.org>
Download mbox | patch
Permalink /patch/9435187/
State New
Headers show

Comments

Johannes Weiner - Nov. 17, 2016, 7:11 p.m.
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@suse.cz>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/khugepaged.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
Kirill A. Shutemov - Nov. 17, 2016, 11:21 p.m.
On Thu, Nov 17, 2016 at 02:11:31PM -0500, 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@suse.cz>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Jan Kara - Nov. 18, 2016, 7:30 a.m.
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@suse.cz>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.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
>

Patch

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;
 			}