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=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_MED,USER_IN_DEF_DKIM_WL 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 96F6AC5CFC0 for ; Mon, 18 Jun 2018 12:57:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 444992086A for ; Mon, 18 Jun 2018 12:57:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="uIfY47Xn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 444992086A Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754565AbeFRM5h (ORCPT ); Mon, 18 Jun 2018 08:57:37 -0400 Received: from mail-pl0-f67.google.com ([209.85.160.67]:35195 "EHLO mail-pl0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754237AbeFRM5g (ORCPT ); Mon, 18 Jun 2018 08:57:36 -0400 Received: by mail-pl0-f67.google.com with SMTP id k1-v6so9011049plt.2 for ; Mon, 18 Jun 2018 05:57:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=9Ov7TBW7BuSNN9tr01UsDeqw26CKjpVgi8DUNvd7IqQ=; b=uIfY47XnhnLaR8/nKlVxsi9AN+XvL/Jdbm6RFANSucSDIH/QFX48Y7TheRjEy+LfyX JKdXPIVYQHhI/nUVF9yr9eBQcQ9OP5K7cmjZERqzuEbHLu8hdK9ReynByIYblAon1T8R yyl84wbHU74+OL5z/7VT8kiicBG7VOjVlpWA6tN2Cg1LPrEx93mxl3xpAPctQIAqiwC4 ISEYXsPjoxE8XZ6PtTI5KbKlEQWfomHRKF+9uwpaNxs8Xw6d5KeJCuXRJvlgtkSJ5i9d 6F1lKhqdasJePzZTAvZ9V+rXHiusGRetQw+PN+fd0qkXii3OgfbT9dj6g4EOiVIXNOt0 gQuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=9Ov7TBW7BuSNN9tr01UsDeqw26CKjpVgi8DUNvd7IqQ=; b=EDPcWkQ+Cz9XJmzxF12Qiq+Ya347xm9h+KIfPbsFnx5CPCLqKy4vYyohRwu8ogfyKw gbbiasXrKXsHz19WMxsye/VW2rmbGb5bJuwY/uJD0Dxb0pRFTSZbv3JLRhz67m8tY6G9 Nyv/ix9qlr1FIq0PCYINO+bx44vF2D4PIn9GpgAeDeDCmqn6MMa3UGlWGTY9/fDhQW1V Qov1/PWvqhbiYgiZpw1T87EhjKpfqdU3OWZtxSH9x+zB9AauyyDu4enEDtkcvLcqpyNp MQadHyJ1vemodxA8ndwItms8rdu2432iE0S92O5ZN+DivkpUl7LT7vdiikXGqIGYHIHR zN+w== X-Gm-Message-State: APt69E2rdv84DWegHJq177mdgSSOZhTjb3saJsD/5IjUv6NF0twffjGH m/sG/jvkm13E2U2JIgT3b2Ni1Q== X-Google-Smtp-Source: ADUXVKKaMdvFEBYDuZvtlyM9O9VJutaVRMrzakbrYAmM1Ykv67wp67SQ9v03eJIYzCUgI+I5dpeBZw== X-Received: by 2002:a17:902:ac89:: with SMTP id h9-v6mr14101442plr.311.1529326655417; Mon, 18 Jun 2018 05:57:35 -0700 (PDT) Received: from localhost ([2620:15c:2c4:201:f5a:7eca:440a:3ead]) by smtp.gmail.com with ESMTPSA id n25-v6sm22238716pff.119.2018.06.18.05.57.34 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 18 Jun 2018 05:57:34 -0700 (PDT) From: Eric Dumazet To: Thomas Gleixner Cc: lkml , Eric Dumazet , Eric Dumazet , Willem de Bruijn Subject: [PATCH] genirq: use rcu in kstat_irqs_usr() Date: Mon, 18 Jun 2018 05:56:12 -0700 Message-Id: <20180618125612.155057-1-edumazet@google.com> X-Mailer: git-send-email 2.18.0.rc1.244.gcf134e6275-goog Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeremy Dorfman identified mutex contention when multiple threads parse /proc/stat concurrently. Since Thomas Gleixner commit 425a5072dcd1 ("genirq: Free irq_desc with rcu"), we can easily switch kstat_irqs_usr() to rcu locking and remove this mutex contetion. show_interrupts() case will be handled in a separate patch. Signed-off-by: Eric Dumazet Reported-by: Jeremy Dorfman Cc: Thomas Gleixner Cc: Willem de Bruijn --- kernel/irq/irqdesc.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c index afc7f902d74a3eff5d1f8a5e407159c5d28625f7..a668b7ad8a5d5e3b191e3a1dc8f9f32293658d42 100644 --- a/kernel/irq/irqdesc.c +++ b/kernel/irq/irqdesc.c @@ -443,6 +443,7 @@ static void free_desc(unsigned int irq) * We free the descriptor, masks and stat fields via RCU. That * allows demultiplex interrupts to do rcu based management of * the child interrupts. + * This also allows us to use rcu in kstat_irqs_usr(). */ call_rcu(&desc->rcu, delayed_free_desc); } @@ -928,17 +929,17 @@ unsigned int kstat_irqs(unsigned int irq) * kstat_irqs_usr - Get the statistics for an interrupt * @irq: The interrupt number * - * Returns the sum of interrupt counts on all cpus since boot for - * @irq. Contrary to kstat_irqs() this can be called from any - * preemptible context. It's protected against concurrent removal of - * an interrupt descriptor when sparse irqs are enabled. + * Returns the sum of interrupt counts on all cpus since boot for @irq. + * Contrary to kstat_irqs() this can be called from any context. + * It uses rcu since a concurrent removal of an interrupt descriptor is + * observing an rcu grace period before delayed_free_desc()/irq_kobj_release(). */ unsigned int kstat_irqs_usr(unsigned int irq) { unsigned int sum; - irq_lock_sparse(); + rcu_read_lock(); sum = kstat_irqs(irq); - irq_unlock_sparse(); + rcu_read_unlock(); return sum; } -- 2.18.0.rc1.244.gcf134e6275-goog