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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 DE096C33CA9 for ; Sun, 12 Jan 2020 08:20:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF61321569 for ; Sun, 12 Jan 2020 08:20:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732398AbgALIUU (ORCPT ); Sun, 12 Jan 2020 03:20:20 -0500 Received: from mx2.suse.de ([195.135.220.15]:35840 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732371AbgALIUU (ORCPT ); Sun, 12 Jan 2020 03:20:20 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 1B2C5B03D; Sun, 12 Jan 2020 08:20:18 +0000 (UTC) Date: Sun, 12 Jan 2020 09:20:17 +0100 Message-ID: From: Takashi Iwai To: Jia-Ju Bai Cc: perex@perex.cz, tiwai@suse.com, rfontana@redhat.com, tglx@linutronix.de, allison@lohutok.net, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt() In-Reply-To: <20200111163027.27135-1-baijiaju1990@gmail.com> References: <20200111163027.27135-1-baijiaju1990@gmail.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 11 Jan 2020 17:30:27 +0100, Jia-Ju Bai wrote: > > The functions snd_cmipci_interrupt() and snd_cmipci_capture_trigger() > may be concurrently executed. > > The function snd_cmipci_capture_trigger() calls > snd_cmipci_pcm_trigger(). In snd_cmipci_pcm_trigger(), the variable > rec->running is written with holding a spinlock cm->reg_lock. But in > snd_cmipci_interrupt(), the identical variable cm->channel[0].running > or cm->channel[1].running is read without holding this spinlock. Thus, > a possible data race may occur. > > To fix this data race, in snd_cmipci_interrupt(), the variables > cm->channel[0].running and cm->channel[1].running are read with holding > the spinlock cm->reg_lock. > > This data race is found by the runtime testing of our tool DILP-2. > > Signed-off-by: Jia-Ju Bai Thanks for the patch. That's indeed a kind of race, but this change won't fix anything in practice, though. The inconsistent running flag between those places, there are two cases: - running became 0 to 1; this cannot happen, as the irq isn't issued before the stream gets started - running became 1 to 0; this means that the stream gets stopped between two points, and it's not better to call snd_pcm_period_elapsed() for an already stopped stream. Takashi > --- > sound/pci/cmipci.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/sound/pci/cmipci.c b/sound/pci/cmipci.c > index dd9d62e2b633..f791152ec48f 100644 > --- a/sound/pci/cmipci.c > +++ b/sound/pci/cmipci.c > @@ -1430,7 +1430,7 @@ static int snd_cmipci_capture_spdif_hw_free(struct snd_pcm_substream *subs) > static irqreturn_t snd_cmipci_interrupt(int irq, void *dev_id) > { > struct cmipci *cm = dev_id; > - unsigned int status, mask = 0; > + unsigned int run_flag0, run_flag1, status, mask = 0; > > /* fastpath out, to ease interrupt sharing */ > status = snd_cmipci_read(cm, CM_REG_INT_STATUS); > @@ -1445,15 +1445,17 @@ static irqreturn_t snd_cmipci_interrupt(int irq, void *dev_id) > mask |= CM_CH1_INT_EN; > snd_cmipci_clear_bit(cm, CM_REG_INT_HLDCLR, mask); > snd_cmipci_set_bit(cm, CM_REG_INT_HLDCLR, mask); > + run_flag0 = cm->channel[0].running; > + run_flag1 = cm->channel[1].running; > spin_unlock(&cm->reg_lock); > > if (cm->rmidi && (status & CM_UARTINT)) > snd_mpu401_uart_interrupt(irq, cm->rmidi->private_data); > > if (cm->pcm) { > - if ((status & CM_CHINT0) && cm->channel[0].running) > + if ((status & CM_CHINT0) && run_flag0) > snd_pcm_period_elapsed(cm->channel[0].substream); > - if ((status & CM_CHINT1) && cm->channel[1].running) > + if ((status & CM_CHINT1) && run_flag1) > snd_pcm_period_elapsed(cm->channel[1].substream); > } > return IRQ_HANDLED; > -- > 2.17.1 >