Commit 4a1c3839 authored by Miaohe Lin's avatar Miaohe Lin Committed by Andrew Morton
Browse files

mm/z3fold: always clear PAGE_CLAIMED under z3fold page lock 

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.

Link: https://lkml.kernel.org/r/20220429064051.61552-8-linmiaohe@huawei.com


Signed-off-by: default avatarMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: default avatarVitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6cf9a349

mm/z3fold.c

+3 −3
Original line number Diff line number Diff line
@@ -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)) {