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=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 03E1CC432BE for ; Thu, 5 Aug 2021 13:27:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E50ED6113C for ; Thu, 5 Aug 2021 13:27:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241699AbhHEN1o (ORCPT ); Thu, 5 Aug 2021 09:27:44 -0400 Received: from mail.efficios.com ([167.114.26.124]:35304 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240827AbhHEN1i (ORCPT ); Thu, 5 Aug 2021 09:27:38 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id ECC9B37088A; Thu, 5 Aug 2021 09:27:23 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id OGouODUyA3ts; Thu, 5 Aug 2021 09:27:23 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 7E4B4370270; Thu, 5 Aug 2021 09:27:23 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 7E4B4370270 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1628170043; bh=Zmyp2Yw12keY0Fl2w34U2wdmnKNqgiqw2zvkTmh7WLI=; h=From:To:Date:Message-Id; b=PnkdBuiNzn8iHo5ztURW7BWT+08VL+yIpQx44W7N14Tn1O7STEwhy7m/4IYOrz/qy A1YdVZwNCBqldTsELQi9fg2kkxSxMtBdBtTHvRbEzpxTHAmNrEOn6bCqOQwJ7wo5si KKtfNPm2396A3EkO/8/sbIydlVBxwpl7JuM4DYuE53SLD3mjX9oZEaWsSJ8AKMS4Ga GcBQaTgtYolwx66sTKUwJxn978ifJNk5z+s438Et9WXAilnViMV4yX7FgJ1TlmY8jg v1MXdvTtHS0yUb1IM/K2LfJW8EXbbLvwnELcmqWieY7XJvL5oOPxAdY9v+RaDozKQu jLCOcaFHDBRvA== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id AeobBf4PIPzE; Thu, 5 Aug 2021 09:27:23 -0400 (EDT) Received: from localhost.localdomain (173-246-27-5.qc.cable.ebox.net [173.246.27.5]) by mail.efficios.com (Postfix) with ESMTPSA id 36D5837054C; Thu, 5 Aug 2021 09:27:23 -0400 (EDT) From: Mathieu Desnoyers To: Steven Rostedt , Ingo Molnar , Peter Zijlstra , Andrew Morton , "Paul E. McKenney" , Stefan Metzmacher , stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers Subject: [PATCH 3/3] Fix: tracepoint: rcu get state and cond sync for static call updates (v2) Date: Thu, 5 Aug 2021 09:27:17 -0400 Message-Id: <20210805132717.23813-4-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210805132717.23813-1-mathieu.desnoyers@efficios.com> References: <20210805132717.23813-1-mathieu.desnoyers@efficios.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org State transitions from 1->0->1 and N->2->1 callbacks require RCU synchronization. Rather than performing the RCU synchronization every time the state change occurs, which is quite slow when many tracepoints are registered in batch, instead keep a snapshot of the RCU state on the most recent transitions which belong to a chain, and conditionally wait for a grace period on the last transition of the chain if one g.p. has not elapsed since the last snapshot. This applies to both RCU and SRCU. Link: https://lore.kernel.org/io-uring/4ebea8f0-58c9-e571-fd30-0ce4f6f09c70@samba.org/ Fixes: d25e37d89dd2 ("tracepoint: Optimize using static_call()") Fixes: 547305a64632 ("tracepoint: Fix out of sync data passing by static caller") Fixes: 352384d5c84e ("tracepoints: Update static_call before tp_funcs when adding a tracepoint") Signed-off-by: Mathieu Desnoyers Reviewed-by: Paul E. McKenney Cc: Steven Rostedt Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Andrew Morton Cc: "Paul E. McKenney" Cc: Stefan Metzmacher Cc: # 5.10+ --- Changes since v1: - Use tp_rcu_get_state/tp_rcu_cond_sync on 2->1 transition when tp_funcs[0].data != old[0].data rather than tracepoint_synchronize_unregister. --- kernel/tracepoint.c | 81 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 69 insertions(+), 12 deletions(-) diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index 8d772bd6894d..d8f69580001c 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -28,6 +28,44 @@ extern tracepoint_ptr_t __stop___tracepoints_ptrs[]; DEFINE_SRCU(tracepoint_srcu); EXPORT_SYMBOL_GPL(tracepoint_srcu); +enum tp_transition_sync { + TP_TRANSITION_SYNC_1_0_1, + TP_TRANSITION_SYNC_N_2_1, + + _NR_TP_TRANSITION_SYNC, +}; + +struct tp_transition_snapshot { + unsigned long rcu; + unsigned long srcu; + bool ongoing; +}; + +/* Protected by tracepoints_mutex */ +static struct tp_transition_snapshot tp_transition_snapshot[_NR_TP_TRANSITION_SYNC]; + +static void tp_rcu_get_state(enum tp_transition_sync sync) +{ + struct tp_transition_snapshot *snapshot = &tp_transition_snapshot[sync]; + + /* Keep the latest get_state snapshot. */ + snapshot->rcu = get_state_synchronize_rcu(); + snapshot->srcu = start_poll_synchronize_srcu(&tracepoint_srcu); + snapshot->ongoing = true; +} + +static void tp_rcu_cond_sync(enum tp_transition_sync sync) +{ + struct tp_transition_snapshot *snapshot = &tp_transition_snapshot[sync]; + + if (!snapshot->ongoing) + return; + cond_synchronize_rcu(snapshot->rcu); + if (!poll_state_synchronize_srcu(&tracepoint_srcu, snapshot->srcu)) + synchronize_srcu(&tracepoint_srcu); + snapshot->ongoing = false; +} + /* Set to 1 to enable tracepoint debug output */ static const int tracepoint_debug; @@ -311,6 +349,11 @@ static int tracepoint_add_func(struct tracepoint *tp, */ switch (nr_func_state(tp_funcs)) { case TP_FUNC_1: /* 0->1 */ + /* + * Make sure new static func never uses old data after a + * 1->0->1 transition sequence. + */ + tp_rcu_cond_sync(TP_TRANSITION_SYNC_1_0_1); /* Set static call to first function */ tracepoint_update_call(tp, tp_funcs); /* Both iterator and static call handle NULL tp->funcs */ @@ -326,9 +369,21 @@ static int tracepoint_add_func(struct tracepoint *tp, * static call update/call. */ rcu_assign_pointer(tp->funcs, tp_funcs); + /* + * Make sure static func never uses incorrect data after a + * 1->...->2->1 transition sequence. + */ + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); break; case TP_FUNC_N: /* N->N+1 (N>1) */ rcu_assign_pointer(tp->funcs, tp_funcs); + /* + * Make sure static func never uses incorrect data after a + * N->...->2->1 (N>1) transition sequence. + */ + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); break; default: WARN_ON_ONCE(1); @@ -372,24 +427,20 @@ static int tracepoint_remove_func(struct tracepoint *tp, /* Both iterator and static call handle NULL tp->funcs */ rcu_assign_pointer(tp->funcs, NULL); /* - * Make sure new func never uses old data after a 1->0->1 - * transition sequence. - * Considering that transition 0->1 is the common case - * and don't have rcu-sync, issue rcu-sync after - * transition 1->0 to break that sequence by waiting for - * readers to be quiescent. + * Make sure new static func never uses old data after a + * 1->0->1 transition sequence. */ - tracepoint_synchronize_unregister(); + tp_rcu_get_state(TP_TRANSITION_SYNC_1_0_1); break; case TP_FUNC_1: /* 2->1 */ rcu_assign_pointer(tp->funcs, tp_funcs); /* - * On 2->1 transition, RCU sync is needed before setting - * static call to first callback, because the observer - * may have loaded any prior tp->funcs after the last one - * associated with an rcu-sync. + * Make sure static func never uses incorrect data after a + * N->...->2->1 (N>2) transition sequence. */ - tracepoint_synchronize_unregister(); + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); + tp_rcu_cond_sync(TP_TRANSITION_SYNC_N_2_1); /* Set static call to first function */ tracepoint_update_call(tp, tp_funcs); break; @@ -397,6 +448,12 @@ static int tracepoint_remove_func(struct tracepoint *tp, fallthrough; case TP_FUNC_N: rcu_assign_pointer(tp->funcs, tp_funcs); + /* + * Make sure static func never uses incorrect data after a + * N->...->2->1 (N>2) transition sequence. + */ + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); break; default: WARN_ON_ONCE(1); -- 2.17.1