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=-8.6 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_SANE_1 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 0D775FA372C for ; Fri, 8 Nov 2019 19:24:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D5A93207FA for ; Fri, 8 Nov 2019 19:24:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573241094; bh=WdMTwF1tMvTKaGQ2zKNu14ZCzIA4ENht4XBnlGbzRDE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=qMeXNXDUPNmcXJw441DOop1OyCI3YFbUz7kz91e1u25UYxW5KDivIjE76iIzKsFJT O3cwYbO1DIxHrYrhOv7JidNb9XeFfmdFH7KDVQpsrLk/B/bVJ3022Cn5y0ZbyGXtNa UT2ki48pqwUz13yv+lZzxgcMRD6JKUmw0KSbZ3lo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731463AbfKHTYx (ORCPT ); Fri, 8 Nov 2019 14:24:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:54712 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730461AbfKHTYx (ORCPT ); Fri, 8 Nov 2019 14:24:53 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [213.233.149.27]) (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 45C2A2067B; Fri, 8 Nov 2019 19:24:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573241091; bh=WdMTwF1tMvTKaGQ2zKNu14ZCzIA4ENht4XBnlGbzRDE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=f2lwSIApoACkQCh24xuonVotpzuhxyurrnHhDAs33TFpEI4qWWDPf2fNyytYr5jCP QMTAXF1UmkK5GhLPP6SbK/Kp127Im9UvPIzvQwnVagvsyOCVfrJ2RJKS8nyvy+pWwO sF9cNTFa78XoMmBWD8XeNAn4BtdnpMsVA9N9QzVg= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 02A4F35204A1; Fri, 8 Nov 2019 11:24:49 -0800 (PST) Date: Fri, 8 Nov 2019 11:24:48 -0800 From: "Paul E. McKenney" To: Eric Dumazet Cc: Thomas Gleixner , linux-kernel , Eric Dumazet Subject: Re: [PATCH 1/2] list: add hlist_unhashed_lockless() Message-ID: <20191108192448.GB20975@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191107193738.195914-1-edumazet@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191107193738.195914-1-edumazet@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote: > 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: "Paul E. McKenney" > Cc: Thomas Gleixner I have queued this, but if you prefer it go some other way: Acked-by: Paul E. McKenney But shouldn't the uses in include/linux/rculist.h also be converted into the patch below? If so, I will squash the following into your patch. Thanx, Paul ------------------------------------------------------------------------ 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) \