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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74E32C433E1 for ; Tue, 25 Aug 2020 14:53:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 591692075F for ; Tue, 25 Aug 2020 14:53:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726929AbgHYOx5 convert rfc822-to-8bit (ORCPT ); Tue, 25 Aug 2020 10:53:57 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:59583 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726856AbgHYOxO (ORCPT ); Tue, 25 Aug 2020 10:53:14 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-97-YtiRwhI8Mw2kXkAIcHOQ7w-1; Tue, 25 Aug 2020 15:53:10 +0100 X-MC-Unique: YtiRwhI8Mw2kXkAIcHOQ7w-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 25 Aug 2020 15:53:10 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Tue, 25 Aug 2020 15:53:10 +0100 From: David Laight To: "linux-kernel@vger.kernel.org" , "'linux-sctp@vger.kernel.org'" , Eric Biggers , 'Marcelo Ricardo Leitner' , 'Catalin Marinas' , "'kent.overstreet@gmail.com'" , Andrew Morton , "'Neil Horman'" Subject: [PATCH 01/13] lib/generic-radix-tree: Fix potentially corrupt tree Thread-Topic: [PATCH 01/13] lib/generic-radix-tree: Fix potentially corrupt tree Thread-Index: AdZ67fPsN9DwMYOhSA+N1EJo6aC85w== Date: Tue, 25 Aug 2020 14:53:10 +0000 Message-ID: <3184cab15fe94db58c7cf3fcf33f3875@AcuMS.aculab.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If the last cmpxchg() done when increasing the tree depth fails (because another caller has done a concurrent update) the 'new_node' is reused later for either a array of pointers or the user data. However the new_node->children[0] has been set non-zero this will either end up being treated as a pointer to another node or as user data. Rather than just setting children[0] = NULL free back the unwanted page in the very unusual case that the cmpxchg() fails. This removes quite a few comparisons from the normal path. Signed-off-by: David Laight --- Although rather nasty not really worth a backport because neither of the 2 places this code is used can possibly hit the failing path. lib/generic-radix-tree.c | 37 +++++++++++++++++-------------------- 1 file changed, 17 insertions(+), 20 deletions(-) diff --git a/lib/generic-radix-tree.c b/lib/generic-radix-tree.c index f25eb111c051..5695fe547f9d 100644 --- a/lib/generic-radix-tree.c +++ b/lib/generic-radix-tree.c @@ -105,7 +105,7 @@ void *__genradix_ptr_alloc(struct __genradix *radix, size_t offset, gfp_t gfp_mask) { struct genradix_root *v = READ_ONCE(radix->root); - struct genradix_node *n, *new_node = NULL; + struct genradix_node *n, *new_node; unsigned level; /* Increase tree depth if necessary: */ @@ -118,20 +118,19 @@ void *__genradix_ptr_alloc(struct __genradix *radix, size_t offset, if (n && ilog2(offset) < genradix_depth_shift(level)) break; - if (!new_node) { - new_node = genradix_alloc_node(gfp_mask); - if (!new_node) - return NULL; - } + new_node = genradix_alloc_node(gfp_mask); + if (!new_node) + return NULL; new_node->children[0] = n; new_root = ((struct genradix_root *) ((unsigned long) new_node | (n ? level + 1 : 0))); - if ((v = cmpxchg_release(&radix->root, r, new_root)) == r) { + v = cmpxchg_release(&radix->root, r, new_root); + if (v == r) v = new_root; - new_node = NULL; - } + else + genradix_free_node(new_node); } while (level--) { @@ -141,20 +140,18 @@ void *__genradix_ptr_alloc(struct __genradix *radix, size_t offset, n = READ_ONCE(*p); if (!n) { - if (!new_node) { - new_node = genradix_alloc_node(gfp_mask); - if (!new_node) - return NULL; - } - - if (!(n = cmpxchg_release(p, NULL, new_node))) - swap(n, new_node); + new_node = genradix_alloc_node(gfp_mask); + if (!new_node) + return NULL; + + n = cmpxchg_release(p, NULL, new_node); + if (!n) + n = new_node; + else + genradix_free_node(new_node); } } - if (new_node) - genradix_free_node(new_node); - return &n->data[offset]; } EXPORT_SYMBOL(__genradix_ptr_alloc); -- 2.25.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)