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 81E8BC43603 for ; Tue, 10 Dec 2019 04:20:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A01A20726 for ; Tue, 10 Dec 2019 04:20:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575951633; bh=om8HX3F1JQk0D3I7aUPL63MWrWDKGacZCIEb5Psjg9Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=WzZM0qOS3dKR7W/hjunPQYRPs4TOhsvlvjJ4lSXJGH6BWPNqpV0sOCKjf4uEVoyH0 jjgLMx5hbXDsqOxbMJt/7QjizqCkBw9a78mHRUWqxpkxu2FQ4sSl2tmuA+TV7WAoZK XDquVY4OjSNE62LuWh6zm/Fmly1YbQ09FOPedn58= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726819AbfLJEUG (ORCPT ); Mon, 9 Dec 2019 23:20:06 -0500 Received: from mail.kernel.org ([198.145.29.99]:46992 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726810AbfLJEUG (ORCPT ); Mon, 9 Dec 2019 23:20:06 -0500 Received: from paulmck-ThinkPad-P72.home (199-192-87-166.static.wiline.com [199.192.87.166]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 232D720836; Tue, 10 Dec 2019 04:20:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575951605; bh=om8HX3F1JQk0D3I7aUPL63MWrWDKGacZCIEb5Psjg9Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=zEUFzaxmNivRQSSB7xxaWvz+8xhj+go/LfiQHyffh1jYDyZ5iHnvV1KkOLuc4MN73 wBvp5xVghYqOqE2bWTfegZbbRHiVQdVJpNHblTgj1SVeF/G3RCgpfMTflfyFMFuAfA Zkfw1/Zxz2iOpc2zJmwCsb9oeCQ+vdEZr/D1l//o= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E . McKenney" Subject: [PATCH tip/core/rcu 2/9] list: Add hlist_unhashed_lockless() Date: Mon, 9 Dec 2019 20:19:55 -0800 Message-Id: <20191210042002.3490-2-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20191210041938.GA3367@paulmck-ThinkPad-P72> References: <20191210041938.GA3367@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: Eric Dumazet We would like to use hlist_unhashed() from timer_pending(), which runs without protection of a lock. Note that other callers might also want to use this variant. Instead of forcing a READ_ONCE() for all hlist_unhashed() callers, add a new helper with an explicit _lockless suffix in the name to better document what is going on. Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head() and hlist_add_before()/hlist_add_behind() to pair with the READ_ONCE(). Signed-off-by: Eric Dumazet Cc: Thomas Gleixner [ paulmck: Also add WRITE_ONCE() to rculist.h. ] Signed-off-by: Paul E. McKenney --- include/linux/list.h | 32 +++++++++++++++++++++----------- include/linux/rculist.h | 24 ++++++++++++------------ 2 files changed, 33 insertions(+), 23 deletions(-) diff --git a/include/linux/list.h b/include/linux/list.h index 85c9255..61f5aaf 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -749,6 +749,16 @@ static inline int hlist_unhashed(const struct hlist_node *h) return !h->pprev; } +/* 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); +} + static inline int hlist_empty(const struct hlist_head *h) { return !READ_ONCE(h->first); @@ -761,7 +771,7 @@ static inline void __hlist_del(struct hlist_node *n) WRITE_ONCE(*pprev, next); if (next) - next->pprev = pprev; + WRITE_ONCE(next->pprev, pprev); } static inline void hlist_del(struct hlist_node *n) @@ -782,32 +792,32 @@ 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; - n->next = first; + WRITE_ONCE(n->next, first); if (first) - first->pprev = &n->next; + WRITE_ONCE(first->pprev, &n->next); WRITE_ONCE(h->first, n); - n->pprev = &h->first; + WRITE_ONCE(n->pprev, &h->first); } /* next must be != NULL */ static inline void hlist_add_before(struct hlist_node *n, struct hlist_node *next) { - n->pprev = next->pprev; - n->next = next; - next->pprev = &n->next; + WRITE_ONCE(n->pprev, next->pprev); + WRITE_ONCE(n->next, next); + WRITE_ONCE(next->pprev, &n->next); WRITE_ONCE(*(n->pprev), n); } static inline void hlist_add_behind(struct hlist_node *n, struct hlist_node *prev) { - n->next = prev->next; - prev->next = n; - n->pprev = &prev->next; + WRITE_ONCE(n->next, prev->next); + WRITE_ONCE(prev->next, n); + WRITE_ONCE(n->pprev, &prev->next); if (n->next) - n->next->pprev = &n->next; + WRITE_ONCE(n->next->pprev, &n->next); } /* after that we'll appear to be on some hlist and hlist_del will work */ diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 61c6728a..4b7ae1b 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -173,7 +173,7 @@ static inline void hlist_del_init_rcu(struct hlist_node *n) { if (!hlist_unhashed(n)) { __hlist_del(n); - n->pprev = NULL; + WRITE_ONCE(n->pprev, NULL); } } @@ -473,7 +473,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, static inline void hlist_del_rcu(struct hlist_node *n) { __hlist_del(n); - n->pprev = LIST_POISON2; + WRITE_ONCE(n->pprev, LIST_POISON2); } /** @@ -489,11 +489,11 @@ static inline void hlist_replace_rcu(struct hlist_node *old, struct hlist_node *next = old->next; new->next = next; - new->pprev = old->pprev; + WRITE_ONCE(new->pprev, old->pprev); rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new); if (next) - new->next->pprev = &new->next; - old->pprev = LIST_POISON2; + WRITE_ONCE(new->next->pprev, &new->next); + WRITE_ONCE(old->pprev, LIST_POISON2); } /* @@ -528,10 +528,10 @@ static inline void hlist_add_head_rcu(struct hlist_node *n, struct hlist_node *first = h->first; n->next = first; - n->pprev = &h->first; + WRITE_ONCE(n->pprev, &h->first); rcu_assign_pointer(hlist_first_rcu(h), n); if (first) - first->pprev = &n->next; + WRITE_ONCE(first->pprev, &n->next); } /** @@ -564,7 +564,7 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n, if (last) { n->next = last->next; - n->pprev = &last->next; + WRITE_ONCE(n->pprev, &last->next); rcu_assign_pointer(hlist_next_rcu(last), n); } else { hlist_add_head_rcu(n, h); @@ -592,10 +592,10 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n, static inline void hlist_add_before_rcu(struct hlist_node *n, struct hlist_node *next) { - n->pprev = next->pprev; + WRITE_ONCE(n->pprev, next->pprev); n->next = next; rcu_assign_pointer(hlist_pprev_rcu(n), n); - next->pprev = &n->next; + WRITE_ONCE(next->pprev, &n->next); } /** @@ -620,10 +620,10 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n, struct hlist_node *prev) { n->next = prev->next; - n->pprev = &prev->next; + WRITE_ONCE(n->pprev, &prev->next); rcu_assign_pointer(hlist_next_rcu(prev), n); if (n->next) - n->next->pprev = &n->next; + WRITE_ONCE(n->next->pprev, &n->next); } #define __hlist_for_each_rcu(pos, head) \ -- 2.9.5