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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25E65C433F5 for ; Tue, 19 Apr 2022 00:04:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237447AbiDSAGl (ORCPT ); Mon, 18 Apr 2022 20:06:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236929AbiDSAGJ (ORCPT ); Mon, 18 Apr 2022 20:06:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3C33B25EB9; Mon, 18 Apr 2022 17:03:28 -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 3DDD9612D2; Tue, 19 Apr 2022 00:03:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49B1BC385C6; Tue, 19 Apr 2022 00:03:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650326605; bh=nNJzJ7ht+CbKYymIkOO+SwWfnhHVpzPdSX+sR/dQxpU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eGOX6Wc1yC7t7X1I1bHokg/oMTHfD1+ZF8aL7evt0quDKJ3mMegJ+f5+92g4fin12 ziRIE8uB49OCyf997rjFW1pwQNTu7BNYv0XqaeltJF0SGSeEjy0wAE0CwpQ7D5Z6PC AIZ1A4ITiS0VA/uzMN2C9xKneCI308C99ci1ykxGU2owmOm5hzP5XKHdDBEwskEhmN t+v2E2mX4Mn/CrI6RKkbpNVppMomRd0vc5w6KQ2tTpgKSQNKgdvwuDC2FvAjQ4CIW+ /g1Swb/v92kQ3FUpYjwiqs3cTIASCcgPgO/ZLMzCLUFnKNHQLPcZSh0EbY8o2SMtIQ 0D1YvYaTgyj1A== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 697FC5C2DF5; Mon, 18 Apr 2022 17:03:24 -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" , Neeraj Upadhyay Subject: [PATCH rcu 16/21] srcu: Create concurrency-safe helper for initiating size transition Date: Mon, 18 Apr 2022 17:03:17 -0700 Message-Id: <20220419000322.3948903-16-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220419000315.GA3948789@paulmck-ThinkPad-P17-Gen-1> References: <20220419000315.GA3948789@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Once there are contention-initiated size transitions, it will be possible for rcutorture to initiate a transition at the same time as a contention-initiated transition. This commit therefore creates a concurrency-safe helper function named srcu_transition_to_big() to safely initiate size transitions. Co-developed-by: Neeraj Upadhyay Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 64993a172cff..c9460374d437 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -272,6 +272,25 @@ EXPORT_SYMBOL_GPL(init_srcu_struct); #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ +/* + * Initiate an idempotent transition to SRCU_SIZE_BIG. + */ +static void srcu_transition_to_big(struct srcu_struct *ssp) +{ + unsigned long flags; + + /* Double-checked locking on ->srcu_size-state. */ + if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL) + return; + spin_lock_irqsave_rcu_node(ssp, flags); + if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL) { + spin_unlock_irqrestore_rcu_node(ssp, flags); + return; + } + smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_ALLOC); + spin_unlock_irqrestore_rcu_node(ssp, flags); +} + /* * First-use initialization of statically allocated srcu_struct * structure. Wiring up the combining tree is more than can be @@ -1523,8 +1542,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) } pr_cont(" T(%ld,%ld)\n", s0, s1); } - if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 2) - WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_ALLOC); + if (convert_to_big == 2) + srcu_transition_to_big(ssp); } EXPORT_SYMBOL_GPL(srcu_torture_stats_print); -- 2.31.1.189.g2e36527f23