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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 984D9C3A59E for ; Wed, 21 Aug 2019 14:03:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 78645206BA for ; Wed, 21 Aug 2019 14:03:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729117AbfHUOC6 (ORCPT ); Wed, 21 Aug 2019 10:02:58 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:55800 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726484AbfHUOC5 (ORCPT ); Wed, 21 Aug 2019 10:02:57 -0400 Received: from p5de0b6c5.dip0.t-ipconnect.de ([93.224.182.197] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1i0RCQ-0005xS-UK; Wed, 21 Aug 2019 16:02:55 +0200 Date: Wed, 21 Aug 2019 16:02:54 +0200 (CEST) From: Thomas Gleixner To: Julien Grall cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, bigeasy@linutronix.de, rostedt@goodmis.org Subject: Re: [RT PATCH 3/3] hrtimer: Prevent using uninitialized spin_lock in hrtimer_grab_expiry_lock() In-Reply-To: <20190821092409.13225-4-julien.grall@arm.com> Message-ID: References: <20190821092409.13225-1-julien.grall@arm.com> <20190821092409.13225-4-julien.grall@arm.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Wed, 21 Aug 2019, Julien Grall wrote: > migration_base is used as a placeholder when an hrtimer is switching > between base (see switch_hrtimer_timer_base). It is possible > theoritically possible to have timer->base equal to migration_base. > > Even if it is a placeholder, it would pass all the current check in > hrtimer_grab_expiry_lock() leading to use softirq_expiry_lock > uninitialized. > > This is can be prevented by checking whether the base is equal to > the placeholder (i.e. migration_base). That's a lame argument. The point is that it does not make sense to do that on migration base, but not for the reason you are giving (uninitialized lock). If base == migration_base then there is no point to lock soft_expiry_lock simply because the timer is not executing the callback in soft irq context and the whole lock/unlock dance can be avoided. But, yes. Good catch. Thanks, tglx