From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00219C433EF for ; Fri, 29 Apr 2022 06:41:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354721AbiD2GoV (ORCPT ); Fri, 29 Apr 2022 02:44:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51928 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354669AbiD2Gnx (ORCPT ); Fri, 29 Apr 2022 02:43:53 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0252BABBD for ; Thu, 28 Apr 2022 23:40:36 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4KqNBf5Dt7z1JBqc; Fri, 29 Apr 2022 14:39:38 +0800 (CST) Received: from huawei.com (10.175.124.27) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 29 Apr 2022 14:40:34 +0800 From: Miaohe Lin To: , CC: , , Subject: [PATCH 8/9] mm/z3fold: fix z3fold_reclaim_page races with z3fold_free Date: Fri, 29 Apr 2022 14:40:50 +0800 Message-ID: <20220429064051.61552-9-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20220429064051.61552-1-linmiaohe@huawei.com> References: <20220429064051.61552-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.124.27] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Think about the below scene: CPU1 CPU2 z3fold_reclaim_page z3fold_free spin_lock(&pool->lock) get_z3fold_header -- hold page_lock kref_get_unless_zero kref_put--zhdr->refcount can be 1 now !z3fold_page_trylock kref_put -- zhdr->refcount is 0 now release_z3fold_page WARN_ON(!list_empty(&zhdr->buddy)); -- we're on buddy now! spin_lock(&pool->lock); -- deadlock here! z3fold_reclaim_page might race with z3fold_free and will lead to pool lock deadlock and zhdr buddy non-empty warning. To fix this, defer getting the refcount until page_lock is held just like what __z3fold_alloc does. Note this has the side effect that we won't break the reclaim if we meet a soon to be released z3fold page now. Fixes: dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim") Signed-off-by: Miaohe Lin --- mm/z3fold.c | 18 +++--------------- 1 file changed, 3 insertions(+), 15 deletions(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index 4a3cd2ff15b0..a7769befd74e 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -519,13 +519,6 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked) atomic64_dec(&pool->pages_nr); } -static void release_z3fold_page(struct kref *ref) -{ - struct z3fold_header *zhdr = container_of(ref, struct z3fold_header, - refcount); - __release_z3fold_page(zhdr, false); -} - static void release_z3fold_page_locked(struct kref *ref) { struct z3fold_header *zhdr = container_of(ref, struct z3fold_header, @@ -1317,12 +1310,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) break; } - if (kref_get_unless_zero(&zhdr->refcount) == 0) { - zhdr = NULL; - break; - } if (!z3fold_page_trylock(zhdr)) { - kref_put(&zhdr->refcount, release_z3fold_page); zhdr = NULL; continue; /* can't evict at this point */ } @@ -1333,14 +1321,14 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) */ if (zhdr->foreign_handles || test_and_set_bit(PAGE_CLAIMED, &page->private)) { - if (!kref_put(&zhdr->refcount, - release_z3fold_page_locked)) - z3fold_page_unlock(zhdr); + z3fold_page_unlock(zhdr); zhdr = NULL; continue; /* can't evict such page */ } list_del_init(&zhdr->buddy); zhdr->cpu = -1; + /* See comment in __z3fold_alloc. */ + kref_get(&zhdr->refcount); break; } -- 2.23.0