From patchwork Wed Aug 21 09:24:07 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Julien Grall X-Patchwork-Id: 171938 Delivered-To: patch@linaro.org Received: by 2002:a92:d204:0:0:0:0:0 with SMTP id y4csp706757ily; Wed, 21 Aug 2019 02:24:19 -0700 (PDT) X-Google-Smtp-Source: APXvYqwu3HiiigiKpBwCYrmk1MWmbzcejDu53+fdlmmnqX6Xv2BWIWmCkI8hYAkIjTuPmIh4IbSA X-Received: by 2002:a63:8ac3:: with SMTP id y186mr28337380pgd.13.1566379459215; Wed, 21 Aug 2019 02:24:19 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1566379459; cv=none; d=google.com; s=arc-20160816; b=k39og8FdTy7QodoN3iTZNa16MIEzawU+RE/TbT4fF8zEAVev01sf5m281DDsfwvQ82 QmwXAlhOeoZ1A03JvKa5L1WZ0wj54fafkvR4C0VOg66fvN7k0Sl8lHS460VSquM9YiVi E5YWOtEW384b1O40ctdHV7miJZqcxS7zQ8V0HPOWAj6woLd4+KhNOkyB807lDxrTKHCH p4QGalNknAFbRtzD/0GC1eFHIcP0Ctgw3UvR+iWMCSZhY1KpcL3zfmiIcIKxRKaMSlse RnnFn5BzvWUVo23cZka6B5SfAS23rEo0x6kht+K6K1w4AbRX7zzxl2T7z3T2G4jZ6zV2 Ohjw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:references:in-reply-to:message-id:date :subject:cc:to:from; bh=rLtCO9zLq+253rBBctzI25rig9xY0QowonHInP78CVI=; b=azMtOzC3PtBk9d8/qYuNhybvayA6Vfm/oxWSD7CrHGnaVqS72aI+JSoZiYLcXPV4WM ByaAlKJ8YuQtn5VbnhkBUUdDdVlQWtfaiSl+922SxWp1qD27CgyiGfT/mqqmUXNSsDXh +fAvZdNmY6wxV4pXLOBp5umy7ym1mhl06VE9jkN6yesnlNaWIa+hB3uNSMi3J6Yanq2d rWG5m/N6zav+8uJd1KMhsg1jnmBpmGtPvRB47560cunj/ojGbVBF/YXU6C1bf0xBZ06h bseWhHEcVIWeOEdT8h7pk0jZvfgKaY+BLwukYSDAzO+UqJB8+7N8po7AsFcuU7GWDSZv 0XBQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id k43si1889580pje.59.2019.08.21.02.24.18; Wed, 21 Aug 2019 02:24:19 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727185AbfHUJYS (ORCPT + 28 others); Wed, 21 Aug 2019 05:24:18 -0400 Received: from foss.arm.com ([217.140.110.172]:55050 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727078AbfHUJYQ (ORCPT ); Wed, 21 Aug 2019 05:24:16 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E2474360; Wed, 21 Aug 2019 02:24:15 -0700 (PDT) Received: from e108454-lin.cambridge.arm.com (e108454-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CD8D63F706; Wed, 21 Aug 2019 02:24:14 -0700 (PDT) From: Julien Grall To: linux-rt-users@vger.kernel.org Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, maz@kernel.org, bigeasy@linutronix.de, rostedt@goodmis.org, Julien Grall Subject: [RT PATCH 1/3] hrtimer: Use READ_ONCE to access timer->base in hrimer_grab_expiry_lock() Date: Wed, 21 Aug 2019 10:24:07 +0100 Message-Id: <20190821092409.13225-2-julien.grall@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20190821092409.13225-1-julien.grall@arm.com> References: <20190821092409.13225-1-julien.grall@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The update to timer->base is protected by the base->cpu_base->lock(). However, hrtimer_grab_expirty_lock() does not access it with the lock. So it would theorically be possible to have timer->base changed under our feet. We need to prevent the compiler to refetch timer->base so the check and the access is performed on the same base. Other access of timer->base are either done with a lock or protected with READ_ONCE(). So use READ_ONCE() in hrtimer_grab_expirty_lock(). Signed-off-by: Julien Grall --- This is rather theoritical so far as I don't have a reproducer for this. --- kernel/time/hrtimer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.11.0 diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 7d7db8802131..b869e816e96a 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -932,7 +932,7 @@ EXPORT_SYMBOL_GPL(hrtimer_forward); void hrtimer_grab_expiry_lock(const struct hrtimer *timer) { - struct hrtimer_clock_base *base = timer->base; + struct hrtimer_clock_base *base = READ_ONCE(timer->base); if (base && base->cpu_base) { spin_lock(&base->cpu_base->softirq_expiry_lock);