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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 C038AC43331 for ; Tue, 24 Mar 2020 13:26:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86F05208C3 for ; Tue, 24 Mar 2020 13:26:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585056365; bh=z5sA3TJymaqiXVItPs92sFSUpzo4nw8D7Z8DxuzeGkU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Gsnn36uQhuDPfIpg/nJxr73DgVsu+nrmXIoKz0j/+W3uFUknwF8uTy/jSea0NRpU4 5wu6KziRUllfVT/sJ2+vPxsvI29L+/bqFL7f88gribAxqUf7FShpGDyz/hgYntq/u4 TbndAqxSmNfCOjaOAv47DRYmJ7JqXh9sEQx5ZoVg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729697AbgCXN0E (ORCPT ); Tue, 24 Mar 2020 09:26:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:50584 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728858AbgCXN0C (ORCPT ); Tue, 24 Mar 2020 09:26:02 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 664EF206F6; Tue, 24 Mar 2020 13:26:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585056361; bh=z5sA3TJymaqiXVItPs92sFSUpzo4nw8D7Z8DxuzeGkU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wLie3Cgpty0zQwIQRrXs78bM0u8QJucH+PSAEOn0ZiW1dhQaej/qOJKv5zuGAnpCl JphmONSI8K/U6nXSrH+U6aWOK+wxNkc1yAmzcdbk7khOgBXjFPs+vbdnLJ7t7Khlcl Mj3weo/AsOwYwSwh1PciDShyfrAVvZvDG31eam2I= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , Linus Torvalds Subject: [PATCH 5.5 098/119] mm: slub: be more careful about the double cmpxchg of freelist Date: Tue, 24 Mar 2020 14:11:23 +0100 Message-Id: <20200324130817.922500997@linuxfoundation.org> X-Mailer: git-send-email 2.25.2 In-Reply-To: <20200324130808.041360967@linuxfoundation.org> References: <20200324130808.041360967@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 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 From: Linus Torvalds commit 5076190daded2197f62fe92cf69674488be44175 upstream. This is just a cleanup addition to Jann's fix to properly update the transaction ID for the slub slowpath in commit fd4d9c7d0c71 ("mm: slub: add missing TID bump.."). The transaction ID is what protects us against any concurrent accesses, but we should really also make sure to make the 'freelist' comparison itself always use the same freelist value that we then used as the new next free pointer. Jann points out that if we do all of this carefully, we could skip the transaction ID update for all the paths that only remove entries from the lists, and only update the TID when adding entries (to avoid the ABA issue with cmpxchg and list handling re-adding a previously seen value). But this patch just does the "make sure to cmpxchg the same value we used" rather than then try to be clever. Acked-by: Jann Horn Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/slub.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/slub.c +++ b/mm/slub.c @@ -2978,11 +2978,13 @@ redo: barrier(); if (likely(page == c->page)) { - set_freepointer(s, tail_obj, c->freelist); + void **freelist = READ_ONCE(c->freelist); + + set_freepointer(s, tail_obj, freelist); if (unlikely(!this_cpu_cmpxchg_double( s->cpu_slab->freelist, s->cpu_slab->tid, - c->freelist, tid, + freelist, tid, head, next_tid(tid)))) { note_cmpxchg_failure("slab_free", s, tid);