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=unavailable 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 65538C43331 for ; Wed, 1 Apr 2020 16:52:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E0222063A for ; Wed, 1 Apr 2020 16:52:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585759957; bh=Y48+j7XGhXX/OxaFoe8wgA3dfctoxSz/8JfDkwkdkEQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=axXA2Meu1oN1srp8wXZaYHg4gTnakzRaRLoXjM40OoBfNNaGFAT2XIvoT68q2EHjZ ilpGwrFUeKLf4kmFyQhVTpI1bNBhB+WdAbhStRRwCZFUlyiIGTws80neunFNDrsVCz npliyL+Qa84vyE9hmaeOti5p4R4Hj1myyJMkN4C4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388762AbgDAQfl (ORCPT ); Wed, 1 Apr 2020 12:35:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:34356 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388322AbgDAQff (ORCPT ); Wed, 1 Apr 2020 12:35:35 -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 79A6B20BED; Wed, 1 Apr 2020 16:35:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585758934; bh=Y48+j7XGhXX/OxaFoe8wgA3dfctoxSz/8JfDkwkdkEQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BdvhjNMWniCG3Phvqz/tI7UpfAuLzP3ULOt/Opdo9/Gwg8PhsCWkK1qol/p17dnAf mNJ1QiZ7YMjpShvBTUYgB52PVisPy+eLhfzdPkKlaDceY2bvOByKmuUX/ki3GExgfZ ge0vcYiL7+FrSR6uK6bAN2BPvD5wHOlih3DyzYOA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , Linus Torvalds Subject: [PATCH 4.9 025/102] mm: slub: be more careful about the double cmpxchg of freelist Date: Wed, 1 Apr 2020 18:17:28 +0200 Message-Id: <20200401161537.757657267@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200401161530.451355388@linuxfoundation.org> References: <20200401161530.451355388@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 @@ -2935,11 +2935,13 @@ 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);