From patchwork Fri Aug 23 21:15:15 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13776032 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F0A8D193418; Fri, 23 Aug 2024 21:15:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724447718; cv=none; b=LK3XqQd2mU/gavERnLhP19UM3jZLa5lynf+JsRrPmQAf41DUFQJCJEvVwK6Pgf9Rm+ZvLT0PrCEwtp4+qOfO1GSekbL+6yVBTOZPxZrXP84vSx7gYRdLgG9y6AHMYOmkyCKGkq7B4qj43bxL2FjkjGTxgGt0wFURzvmOk6Ob5ZM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724447718; c=relaxed/simple; bh=DkzXOO64SLa1CEcGq1E7i7N2RHxWUUhHE+4zJSeNSXs=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=gz+zBpkGUNz9cyt+Q8KY4hiomZbLpH010Kk2eXGjYLBKKws3FYBfXonsNVdmOigVS0Vc+cxMDr0miGd7GSXVjx3vOV4vfu1Nfu/6072uzEM92SJKAb7/XhpX01+JgBiIs+7uI/CDFkNoIqcbcJ6aNKYJ6GQSdlNJmn/cCFm93BY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QaszPb+v; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QaszPb+v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92226C4AF09; Fri, 23 Aug 2024 21:15:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724447717; bh=DkzXOO64SLa1CEcGq1E7i7N2RHxWUUhHE+4zJSeNSXs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QaszPb+vaUVvWuE2DRZp5kCrLS+hlEqGHJfKBZ3MOe3eLi9Z8CrreKOSnqTW1vvdC zDvys+w7qOTBkui2HcNri7fe+WH2a+6UbWf43QMmcsTmpj8Gsqfq28KLiytQTM1ABW P1x+QAgHsjcl1GwfLussyEosiJTZH67puX2tFbM377JZcNMboIT0SUozTb5W8k7+Q0 XodxgrNoWSvq9NdDH7wgRI/HtfKJgh/z1/12E13edOLwez7h8yMbaP6UEP5F9xNYCr UKylE0dWHpYphUXYW7D+FqRvrSO0wkgvF2em6QUceJmCCzX47YswNylgTTXaGlIstt YFo3FNAAZhYUw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 2F8A7CE14F4; Fri, 23 Aug 2024 14:15:17 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, riel@surriel.com, "Paul E. McKenney" Subject: [PATCH rcu 4/4] rcu: Finer-grained grace-period-end checks in rcu_dump_cpu_stacks() Date: Fri, 23 Aug 2024 14:15:15 -0700 Message-Id: <20240823211516.2984627-4-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <415b108b-1046-4027-aa2a-c829b77f39f6@paulmck-laptop> References: <415b108b-1046-4027-aa2a-c829b77f39f6@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 This commit pushes the grace-period-end checks further down into rcu_dump_cpu_stacks(), and also uses lockless checks coupled with finer-grained locking. The result is that the current leaf rcu_node structure's ->lock is acquired only if a stack backtrace might be needed from the current CPU, and is held across only that CPU's backtrace. As a result, if there are no stalled CPUs associated with a given rcu_node structure, then its ->lock will not be acquired at all. On large systems, it is usually (though not always) the case that a small number of CPUs are stalling the current grace period, which means that the ->lock need be acquired only for a small fraction of the rcu_node structures. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_stall.h | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 9c8eb4b8dfb33..ab6848baba4f6 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -341,20 +341,24 @@ static void rcu_dump_cpu_stacks(unsigned long gp_seq) struct rcu_node *rnp; rcu_for_each_leaf_node(rnp) { - if (gp_seq != rcu_state.gp_seq) { - pr_err("INFO: Stall ended during stack backtracing.\n"); - return; - } printk_deferred_enter(); - raw_spin_lock_irqsave_rcu_node(rnp, flags); - for_each_leaf_node_possible_cpu(rnp, cpu) + for_each_leaf_node_possible_cpu(rnp, cpu) { + if (gp_seq != data_race(rcu_state.gp_seq)) { + printk_deferred_exit(); + pr_err("INFO: Stall ended during stack backtracing.\n"); + return; + } + if (!(data_race(rnp->qsmask) & leaf_node_cpu_bit(rnp, cpu))) + continue; + raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { if (cpu_is_offline(cpu)) pr_err("Offline CPU %d blocking current GP.\n", cpu); else dump_cpu_task(cpu); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } printk_deferred_exit(); } }