linux-kernel - [PATCH 7/9] mm/z3fold: always clear PAGE

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Message-ID: <20220429064051.61552-8-linmiaohe@huawei.com>
Date:   Fri, 29 Apr 2022 14:40:49 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>, <vitaly.wool@...sulko.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH 7/9] 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.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.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)) {
-- 
2.23.0