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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 7B83CC43331 for ; Tue, 24 Mar 2020 15:37:21 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id CEF36208CA for ; Tue, 24 Mar 2020 15:37:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="P4WUrxom" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CEF36208CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18158-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 24042 invoked by uid 550); 24 Mar 2020 15:37:06 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 23883 invoked from network); 24 Mar 2020 15:37:05 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585064213; bh=BUHldg+uHWPMoaQQxKAqgDLVXAxhSWfg2Skor2EJDJQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=P4WUrxomxUjXLQ55G79FEXsia4jVbj/FyMmNGUtO5rB6aRs6GC2p4eXU79n+i0dS3 JJ7iZvQS2mTvMGK8oWhM8HrzfM8TBNf118/tWXwjOLlwEWJMjvTnPJnr/4b8W4os23 d3iXDnXYlCQrqwHtfhwPduvfQjOsUg4r1fFCkDqY= From: Will Deacon To: linux-kernel@vger.kernel.org Cc: Will Deacon , Eric Dumazet , Jann Horn , Kees Cook , Maddie Stone , Marco Elver , "Paul E . McKenney" , Peter Zijlstra , Thomas Gleixner , kernel-team@android.com, kernel-hardening@lists.openwall.com Subject: [RFC PATCH 01/21] list: Remove hlist_unhashed_lockless() Date: Tue, 24 Mar 2020 15:36:23 +0000 Message-Id: <20200324153643.15527-2-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200324153643.15527-1-will@kernel.org> References: <20200324153643.15527-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit c54a2744497d ("list: Add hlist_unhashed_lockless()") added a "lockless" variant of hlist_unhashed() that uses READ_ONCE() to access the 'pprev' pointer of the 'hlist_node', the intention being that this could be used by 'timer_pending()' to silence a KCSAN warning. As well as forgetting to add the caller, the patch also sprinkles {READ,WRITE}_ONCE() invocations over the standard (i.e. non-RCU) hlist code, which is undesirable for a number of reasons: 1. It gives the misleading impression that the non-RCU hlist code is in some way lock-free (despite the notable absence of any memory barriers!) and silences KCSAN in such cases. 2. It unnecessarily penalises code generation for non-RCU hlist users 3. It makes it difficult to introduce list integrity checks because of the possibility of concurrent callers. Retain the {READ,WRITE}_ONCE() invocations for the RCU hlist code, but remove them from the non-RCU implementation. Remove the unused 'hlist_unhashed_lockless()' function entirely and add the READ_ONCE() to hlist_unhashed(), as we do already for hlist_empty() already. Cc: Eric Dumazet Cc: Thomas Gleixner Cc: Paul E. McKenney Cc: Peter Zijlstra Signed-off-by: Will Deacon --- include/linux/list.h | 33 ++++++++++----------------------- 1 file changed, 10 insertions(+), 23 deletions(-) diff --git a/include/linux/list.h b/include/linux/list.h index 884216db3246..4fed5a0f9b77 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -777,19 +777,6 @@ static inline void INIT_HLIST_NODE(struct hlist_node *h) * node in unhashed state, but hlist_nulls_del() does not. */ static inline int hlist_unhashed(const struct hlist_node *h) -{ - return !h->pprev; -} - -/** - * hlist_unhashed_lockless - Version of hlist_unhashed for lockless use - * @h: Node to be checked - * - * This variant of hlist_unhashed() must be used in lockless contexts - * to avoid potential load-tearing. The READ_ONCE() is paired with the - * various WRITE_ONCE() in hlist helpers that are defined below. - */ -static inline int hlist_unhashed_lockless(const struct hlist_node *h) { return !READ_ONCE(h->pprev); } @@ -852,11 +839,11 @@ static inline void hlist_del_init(struct hlist_node *n) static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h) { struct hlist_node *first = h->first; - WRITE_ONCE(n->next, first); + n->next = first; if (first) - WRITE_ONCE(first->pprev, &n->next); + first->pprev = &n->next; WRITE_ONCE(h->first, n); - WRITE_ONCE(n->pprev, &h->first); + n->pprev = &h->first; } /** @@ -867,9 +854,9 @@ static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h) static inline void hlist_add_before(struct hlist_node *n, struct hlist_node *next) { - WRITE_ONCE(n->pprev, next->pprev); - WRITE_ONCE(n->next, next); - WRITE_ONCE(next->pprev, &n->next); + n->pprev = next->pprev; + n->next = next; + next->pprev = &n->next; WRITE_ONCE(*(n->pprev), n); } @@ -881,12 +868,12 @@ static inline void hlist_add_before(struct hlist_node *n, static inline void hlist_add_behind(struct hlist_node *n, struct hlist_node *prev) { - WRITE_ONCE(n->next, prev->next); - WRITE_ONCE(prev->next, n); - WRITE_ONCE(n->pprev, &prev->next); + n->next = prev->next; + prev->next = n; + n->pprev = &prev->next; if (n->next) - WRITE_ONCE(n->next->pprev, &n->next); + n->next->pprev = &n->next; } /** -- 2.20.1