From patchwork Wed Oct 19 22:58:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13012470 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B3EEC433FE for ; Wed, 19 Oct 2022 22:58:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231128AbiJSW6v (ORCPT ); Wed, 19 Oct 2022 18:58:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230440AbiJSW6u (ORCPT ); Wed, 19 Oct 2022 18:58:50 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02D8A1CBA94; Wed, 19 Oct 2022 15:58:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9195D61920; Wed, 19 Oct 2022 22:58:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA56CC433C1; Wed, 19 Oct 2022 22:58:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666220328; bh=lC2ZhkuunFA2ksKMDckPtMceJ6zVcRmtLkRgyIgtcls=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cnfRlwEud8zypsIPnkwkCkn4HzzhbvLYXCgPFisO8zPb3C9evnYf+kZ3SQCxwnJHu 5R9xpAjW3LITHmqT4vuhUGiA6f3pnLgLI1uyh2NP3h/sgiOfkqgUUb+PO5BAhzptBn dgGpyTdlk4eBWNcDLem7An8S6TbmugUekGrA3uLk1rv/K6gNaoJ416WnYw19pRhroW 7rXKmCMtL/u2/czbqQraIF1CRXk/WWpE2VQqm3SVOyUOt393LxO9arF800iV3GXnmN jEEvmzO5mbnEppwdS85MqBgABaBfTg783962fITifkN43P+5H2drvNoQk4319L54O+ oGF8SQRQ88njA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id AA4CD5C06B4; Wed, 19 Oct 2022 15:58:47 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, "Paul E. McKenney" , Frederic Weisbecker , Thomas Gleixner , John Ogness , Petr Mladek Subject: [PATCH v3 rcu 01/11] srcu: Convert ->srcu_lock_count and ->srcu_unlock_count to atomic Date: Wed, 19 Oct 2022 15:58:36 -0700 Message-Id: <20221019225846.2501109-1-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221019225838.GA2500612@paulmck-ThinkPad-P17-Gen-1> References: <20221019225838.GA2500612@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org NMI-safe variants of srcu_read_lock() and srcu_read_unlock() are needed by printk(), which on many architectures entails read-modify-write atomic operations. This commit prepares Tree SRCU for this change by making both ->srcu_lock_count and ->srcu_unlock_count by atomic_long_t. [ paulmck: Apply feedback from John Ogness. ] Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/ Signed-off-by: Paul E. McKenney Reviewed-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: John Ogness Cc: Petr Mladek --- include/linux/srcutree.h | 4 ++-- kernel/rcu/srcutree.c | 24 ++++++++++++------------ 2 files changed, 14 insertions(+), 14 deletions(-) diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index e3014319d1ade..0c4eca07d78d5 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -23,8 +23,8 @@ struct srcu_struct; */ struct srcu_data { /* Read-side state. */ - unsigned long srcu_lock_count[2]; /* Locks per CPU. */ - unsigned long srcu_unlock_count[2]; /* Unlocks per CPU. */ + atomic_long_t srcu_lock_count[2]; /* Locks per CPU. */ + atomic_long_t srcu_unlock_count[2]; /* Unlocks per CPU. */ /* Update-side state. */ spinlock_t __private lock ____cacheline_internodealigned_in_smp; diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 1c304fec89c02..25e9458da6a26 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -417,7 +417,7 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx) for_each_possible_cpu(cpu) { struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); - sum += READ_ONCE(cpuc->srcu_lock_count[idx]); + sum += atomic_long_read(&cpuc->srcu_lock_count[idx]); } return sum; } @@ -434,7 +434,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx) for_each_possible_cpu(cpu) { struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); - sum += READ_ONCE(cpuc->srcu_unlock_count[idx]); + sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]); } return sum; } @@ -503,10 +503,10 @@ static bool srcu_readers_active(struct srcu_struct *ssp) for_each_possible_cpu(cpu) { struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); - sum += READ_ONCE(cpuc->srcu_lock_count[0]); - sum += READ_ONCE(cpuc->srcu_lock_count[1]); - sum -= READ_ONCE(cpuc->srcu_unlock_count[0]); - sum -= READ_ONCE(cpuc->srcu_unlock_count[1]); + sum += atomic_long_read(&cpuc->srcu_lock_count[0]); + sum += atomic_long_read(&cpuc->srcu_lock_count[1]); + sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]); + sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]); } return sum; } @@ -636,7 +636,7 @@ int __srcu_read_lock(struct srcu_struct *ssp) int idx; idx = READ_ONCE(ssp->srcu_idx) & 0x1; - this_cpu_inc(ssp->sda->srcu_lock_count[idx]); + this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); smp_mb(); /* B */ /* Avoid leaking the critical section. */ return idx; } @@ -650,7 +650,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock); void __srcu_read_unlock(struct srcu_struct *ssp, int idx) { smp_mb(); /* C */ /* Avoid leaking the critical section. */ - this_cpu_inc(ssp->sda->srcu_unlock_count[idx]); + this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter); } EXPORT_SYMBOL_GPL(__srcu_read_unlock); @@ -1687,8 +1687,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) struct srcu_data *sdp; sdp = per_cpu_ptr(ssp->sda, cpu); - u0 = data_race(sdp->srcu_unlock_count[!idx]); - u1 = data_race(sdp->srcu_unlock_count[idx]); + u0 = data_race(atomic_long_read(&sdp->srcu_unlock_count[!idx])); + u1 = data_race(atomic_long_read(&sdp->srcu_unlock_count[idx])); /* * Make sure that a lock is always counted if the corresponding @@ -1696,8 +1696,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) */ smp_rmb(); - l0 = data_race(sdp->srcu_lock_count[!idx]); - l1 = data_race(sdp->srcu_lock_count[idx]); + l0 = data_race(atomic_long_read(&sdp->srcu_lock_count[!idx])); + l1 = data_race(atomic_long_read(&sdp->srcu_lock_count[idx])); c0 = l0 - u0; c1 = l1 - u1;