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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 66F45C64E7C for ; Sat, 21 Nov 2020 00:59:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3413923A6B for ; Sat, 21 Nov 2020 00:59:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="z3ecfHMz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728960AbgKUA7d (ORCPT ); Fri, 20 Nov 2020 19:59:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:37514 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728462AbgKUA7W (ORCPT ); Fri, 20 Nov 2020 19:59:22 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (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 57C452415A; Sat, 21 Nov 2020 00:59:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605920361; bh=W/S2m/VadUOhISjmRqts6KrTfwpyKxEGsMBt8JeMGZs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=z3ecfHMzmKO6GDuqD1KLvf9TTeqIDDB85TQfX8J6u7M/sGx2jpfZPR3H7M0FIvaPT /r0hRh/MJ3GTw+k10jRexPKx++qNddJT/Ms+M1HbI+H5XWxu1gEZxaFhdCed2HpjGi 2+Sl02j4y01vAn/u/LArFaWbYSDh3bgtrBUbvwh8= 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, 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, kent.overstreet@gmail.com, "Paul E. McKenney" Subject: [PATCH v2 tip/core/rcu 3/6] srcu: Provide internal interface to start a Tree SRCU grace period Date: Fri, 20 Nov 2020 16:59:16 -0800 Message-Id: <20201121005919.17152-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <@@@> References: <@@@> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" There is a need for a polling interface for SRCU grace periods. This polling needs to initiate an SRCU grace period without having to queue (and manage) a callback. This commit therefore splits the Tree SRCU __call_srcu() function into callback-initialization and queuing/start-grace-period portions, with the latter in a new function named srcu_gp_start_if_needed(). This function may be passed a NULL callback pointer, in which case it will refrain from queuing anything. Why have the new function mess with queuing? Locking considerations, of course! Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ Reported-by: Kent Overstreet Reviewed-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 66 +++++++++++++++++++++++++++++---------------------- 1 file changed, 37 insertions(+), 29 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 79b7081..d930ece 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -808,6 +808,42 @@ static void srcu_leak_callback(struct rcu_head *rhp) } /* + * Start an SRCU grace period, and also queue the callback if non-NULL. + */ +static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rhp, bool do_norm) +{ + unsigned long flags; + int idx; + bool needexp = false; + bool needgp = false; + unsigned long s; + struct srcu_data *sdp; + + idx = srcu_read_lock(ssp); + sdp = raw_cpu_ptr(ssp->sda); + spin_lock_irqsave_rcu_node(sdp, flags); + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&ssp->srcu_gp_seq)); + s = rcu_seq_snap(&ssp->srcu_gp_seq); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s); + if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { + sdp->srcu_gp_seq_needed = s; + needgp = true; + } + if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { + sdp->srcu_gp_seq_needed_exp = s; + needexp = true; + } + spin_unlock_irqrestore_rcu_node(sdp, flags); + if (needgp) + srcu_funnel_gp_start(ssp, sdp, s, do_norm); + else if (needexp) + srcu_funnel_exp_start(ssp, sdp->mynode, s); + srcu_read_unlock(ssp, idx); +} + +/* * Enqueue an SRCU callback on the srcu_data structure associated with * the current CPU and the specified srcu_struct structure, initiating * grace-period processing if it is not already running. @@ -838,13 +874,6 @@ static void srcu_leak_callback(struct rcu_head *rhp) static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func, bool do_norm) { - unsigned long flags; - int idx; - bool needexp = false; - bool needgp = false; - unsigned long s; - struct srcu_data *sdp; - check_init_srcu_struct(ssp); if (debug_rcu_head_queue(rhp)) { /* Probable double call_srcu(), so leak the callback. */ @@ -853,28 +882,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, return; } rhp->func = func; - idx = srcu_read_lock(ssp); - sdp = raw_cpu_ptr(ssp->sda); - spin_lock_irqsave_rcu_node(sdp, flags); - rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); - rcu_segcblist_advance(&sdp->srcu_cblist, - rcu_seq_current(&ssp->srcu_gp_seq)); - s = rcu_seq_snap(&ssp->srcu_gp_seq); - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s); - if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { - sdp->srcu_gp_seq_needed = s; - needgp = true; - } - if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { - sdp->srcu_gp_seq_needed_exp = s; - needexp = true; - } - spin_unlock_irqrestore_rcu_node(sdp, flags); - if (needgp) - srcu_funnel_gp_start(ssp, sdp, s, do_norm); - else if (needexp) - srcu_funnel_exp_start(ssp, sdp->mynode, s); - srcu_read_unlock(ssp, idx); + srcu_gp_start_if_needed(ssp, rhp, do_norm); } /** -- 2.9.5