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: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/z3fold.c b/mm/z3fold.c
index a1c150f..4a3cd2f 100644 (file)
--- 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 @@ next:
                        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)) {