diff mbox series

[7/9] mm/z3fold: always clear PAGE_CLAIMED under z3fold page lock

Message ID 20220429064051.61552-8-linmiaohe@huawei.com (mailing list archive)
State New
Headers show
Series A few fixup patches for z3fold | expand

Commit Message

Miaohe Lin April 29, 2022, 6:40 a.m. UTC
Think about the below race window:

CPU1				CPU2
z3fold_reclaim_page		z3fold_free
 test_and_set_bit PAGE_CLAIMED
 failed to reclaim page
 z3fold_page_lock(zhdr);
 add back to the lru list;
 z3fold_page_unlock(zhdr);
				 get_z3fold_header
				 page_claimed=test_and_set_bit PAGE_CLAIMED

 clear_bit(PAGE_CLAIMED, &page->private);

				 if (!page_claimed) /* it's false true */
				  free_handle is not called

free_handle won't be called in this case. So z3fold_buddy_slots will leak.
Fix it by always clear PAGE_CLAIMED under z3fold page lock.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/z3fold.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Vitaly Wool May 19, 2022, 7:14 a.m. UTC | #1
On Fri, Apr 29, 2022 at 8:40 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> Think about the below race window:
>
> CPU1                            CPU2
> z3fold_reclaim_page             z3fold_free
>  test_and_set_bit PAGE_CLAIMED
>  failed to reclaim page
>  z3fold_page_lock(zhdr);
>  add back to the lru list;
>  z3fold_page_unlock(zhdr);
>                                  get_z3fold_header
>                                  page_claimed=test_and_set_bit PAGE_CLAIMED
>
>  clear_bit(PAGE_CLAIMED, &page->private);
>
>                                  if (!page_claimed) /* it's false true */
>                                   free_handle is not called
>
> free_handle won't be called in this case. So z3fold_buddy_slots will leak.
> Fix it by always clear PAGE_CLAIMED under z3fold page lock.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/z3fold.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index a1c150fc8def..4a3cd2ff15b0 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1221,8 +1221,8 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>                 return;
>         }
>         if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
> -               put_z3fold_header(zhdr);
>                 clear_bit(PAGE_CLAIMED, &page->private);
> +               put_z3fold_header(zhdr);
>                 return;
>         }
>         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
> @@ -1424,8 +1424,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>                         spin_unlock(&pool->lock);
>                         if (list_empty(&zhdr->buddy))
>                                 add_to_unbuddied(pool, zhdr);
> -                       z3fold_page_unlock(zhdr);
>                         clear_bit(PAGE_CLAIMED, &page->private);
> +                       z3fold_page_unlock(zhdr);
>                 }
>
>                 /* We started off locked to we need to lock the pool back */
> @@ -1577,8 +1577,8 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
>         if (!z3fold_page_trylock(zhdr))
>                 return -EAGAIN;
>         if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) {
> -               z3fold_page_unlock(zhdr);
>                 clear_bit(PAGE_CLAIMED, &page->private);
> +               z3fold_page_unlock(zhdr);
>                 return -EBUSY;
>         }
>         if (work_pending(&zhdr->work)) {

Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
> --
> 2.23.0
>
diff mbox series

Patch

diff --git a/mm/z3fold.c b/mm/z3fold.c
index a1c150fc8def..4a3cd2ff15b0 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1221,8 +1221,8 @@  static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 		return;
 	}
 	if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
-		put_z3fold_header(zhdr);
 		clear_bit(PAGE_CLAIMED, &page->private);
+		put_z3fold_header(zhdr);
 		return;
 	}
 	if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
@@ -1424,8 +1424,8 @@  static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 			spin_unlock(&pool->lock);
 			if (list_empty(&zhdr->buddy))
 				add_to_unbuddied(pool, zhdr);
-			z3fold_page_unlock(zhdr);
 			clear_bit(PAGE_CLAIMED, &page->private);
+			z3fold_page_unlock(zhdr);
 		}
 
 		/* We started off locked to we need to lock the pool back */
@@ -1577,8 +1577,8 @@  static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
 	if (!z3fold_page_trylock(zhdr))
 		return -EAGAIN;
 	if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) {
-		z3fold_page_unlock(zhdr);
 		clear_bit(PAGE_CLAIMED, &page->private);
+		z3fold_page_unlock(zhdr);
 		return -EBUSY;
 	}
 	if (work_pending(&zhdr->work)) {