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,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 5B17BC63798 for ; Sat, 21 Nov 2020 00:59:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0E61023A65 for ; Sat, 21 Nov 2020 00:59:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="LnIINm8y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728872AbgKUA7Y (ORCPT ); Fri, 20 Nov 2020 19:59:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:37586 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728578AbgKUA7X (ORCPT ); Fri, 20 Nov 2020 19:59:23 -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 C565824178; 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=kjoDqIAuB2YrUu54UnWe2QrcIRZi2zrEtlR8yBGVGkY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LnIINm8ynGA92bRiU7N24F0Wt1rA6ISLTiYP+rFpUMV9Kld0zAn4AoCW02RLCfoey b1ENA6cmKim4m9+t4gQPQjsdxcva4gt4QrJvJvs5DqjvxV1ZysRUELkUgw6txWdNfk ycgvyC+zIE6PxtZjfDBk+WA74j5qdxdq4XHlFsiE= 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 5/6] srcu: Provide polling interfaces for Tree SRCU grace periods Date: Fri, 20 Nov 2020 16:59:18 -0800 Message-Id: <20201121005919.17152-5-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, so this commit supplies get_state_synchronize_srcu(), start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() for this purpose. The first can be used if future grace periods are inevitable (perhaps due to a later call_srcu() invocation), the second if future grace periods might not otherwise happen, and the third to check if a grace period has elapsed since the corresponding call to either of the first two. As with get_state_synchronize_rcu() and cond_synchronize_rcu(), the return value from either get_state_synchronize_srcu() or start_poll_synchronize_srcu() must be passed in to a later call to poll_state_synchronize_srcu(). Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ Reported-by: Kent Overstreet [ paulmck: Add EXPORT_SYMBOL_GPL() per kernel test robot feedback. ] [ paulmck: Apply feedback from Neeraj Upadhyay. ] Link: https://lore.kernel.org/lkml/20201117004017.GA7444@paulmck-ThinkPad-P72/ Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutiny.c | 2 +- kernel/rcu/srcutree.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 64 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index b073175..c8f4202 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -148,7 +148,7 @@ void srcu_drive_gp(struct work_struct *wp) * straighten that out. */ WRITE_ONCE(ssp->srcu_gp_running, false); - if (USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) + if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) schedule_work(&ssp->srcu_work); } EXPORT_SYMBOL_GPL(srcu_drive_gp); diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d930ece..945c047 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -810,7 +810,8 @@ 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) +static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, + struct rcu_head *rhp, bool do_norm) { unsigned long flags; int idx; @@ -819,10 +820,12 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh unsigned long s; struct srcu_data *sdp; + check_init_srcu_struct(ssp); 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); + if (rhp) + 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); @@ -841,6 +844,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh else if (needexp) srcu_funnel_exp_start(ssp, sdp->mynode, s); srcu_read_unlock(ssp, idx); + return s; } /* @@ -874,7 +878,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func, bool do_norm) { - check_init_srcu_struct(ssp); if (debug_rcu_head_queue(rhp)) { /* Probable double call_srcu(), so leak the callback. */ WRITE_ONCE(rhp->func, srcu_leak_callback); @@ -882,7 +885,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, return; } rhp->func = func; - srcu_gp_start_if_needed(ssp, rhp, do_norm); + (void)srcu_gp_start_if_needed(ssp, rhp, do_norm); } /** @@ -1011,6 +1014,62 @@ void synchronize_srcu(struct srcu_struct *ssp) } EXPORT_SYMBOL_GPL(synchronize_srcu); +/** + * get_state_synchronize_srcu - Provide an end-of-grace-period cookie + * @ssp: srcu_struct to provide cookie for. + * + * This function returns a cookie that can be passed to + * poll_state_synchronize_srcu(), which will return true if a full grace + * period has elapsed in the meantime. It is the caller's responsibility + * to make sure that grace period happens, for example, by invoking + * call_srcu() after return from get_state_synchronize_srcu(). + */ +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) +{ + // Any prior manipulation of SRCU-protected data must happen + // before the load from ->srcu_gp_seq. + smp_mb(); + return rcu_seq_snap(&ssp->srcu_gp_seq); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); + +/** + * start_poll_synchronize_srcu - Provide cookie and start grace period + * @ssp: srcu_struct to provide cookie for. + * + * This function returns a cookie that can be passed to + * poll_state_synchronize_srcu(), which will return true if a full grace + * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(), + * this function also ensures that any needed SRCU grace period will be + * started. This convenience does come at a cost in terms of CPU overhead. + */ +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) +{ + return srcu_gp_start_if_needed(ssp, NULL, true); +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); + +/** + * poll_state_synchronize_srcu - Has cookie's grace period ended? + * @ssp: srcu_struct to provide cookie for. + * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu(). + * + * This function takes the cookie that was returned from either + * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and + * returns @true if an SRCU grace period elapsed since the time that the + * cookie was created. + */ +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) +{ + if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie)) + return false; + // Ensure that the end of the SRCU grace period happens before + // any subsequent code that the caller might execute. + smp_mb(); // ^^^ + return true; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); + /* * Callback function for srcu_barrier() use. */ -- 2.9.5