From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751780AbbASJtE (ORCPT ); Mon, 19 Jan 2015 04:49:04 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50529 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751403AbbASJtC (ORCPT ); Mon, 19 Jan 2015 04:49:02 -0500 Date: Mon, 19 Jan 2015 10:49:01 +0100 Message-ID: From: Takashi Iwai To: Jiri Slaby Cc: linux-kernel@vger.kernel.org, Jaroslav Kysela , alsa-devel@alsa-project.org Subject: Re: [PATCH 3/3] sound: dummy, avoid races with timer In-Reply-To: <1421660576-8435-3-git-send-email-jslaby@suse.cz> References: <1421660576-8435-1-git-send-email-jslaby@suse.cz> <1421660576-8435-3-git-send-email-jslaby@suse.cz> 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/24.4 (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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org At Mon, 19 Jan 2015 10:42:56 +0100, Jiri Slaby wrote: > > There is a race between timer and process contexts. Process context > does not disable irqs, so when a timer ticks inside process' critical > section, the system can deadlock. Fix this by a traditional _irqsave > variant of spin_lock. > > Signed-off-by: Jiri Slaby > Cc: Jaroslav Kysela > Cc: Takashi Iwai > Cc: alsa-devel@alsa-project.org > --- > sound/drivers/dummy.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c > index 6d6bf4093583..18a7cfc99078 100644 > --- a/sound/drivers/dummy.c > +++ b/sound/drivers/dummy.c > @@ -271,10 +271,13 @@ static void dummy_systimer_update(struct dummy_systimer_pcm *dpcm) > static int dummy_systimer_start(struct snd_pcm_substream *substream) > { > struct dummy_systimer_pcm *dpcm = substream->runtime->private_data; > - spin_lock(&dpcm->lock); > + unsigned long flags; > + > + spin_lock_irqsave(&dpcm->lock, flags); > dpcm->base_time = jiffies; > dummy_systimer_rearm(dpcm); > - spin_unlock(&dpcm->lock); > + spin_unlock_irqrestore(&dpcm->lock, flags); > + This looks correct, but... > return 0; > } > > @@ -322,12 +325,14 @@ static snd_pcm_uframes_t > dummy_systimer_pointer(struct snd_pcm_substream *substream) > { > struct dummy_systimer_pcm *dpcm = substream->runtime->private_data; > + unsigned long flags; > snd_pcm_uframes_t pos; > > - spin_lock(&dpcm->lock); > + spin_lock_irqsave(&dpcm->lock, flags); > dummy_systimer_update(dpcm); > pos = dpcm->frac_pos / HZ; > - spin_unlock(&dpcm->lock); > + spin_unlock_irqrestore(&dpcm->lock, flags); > + This chunk is superfluous. The pointer callback is guaranteed to be called in the irq-disabled context. thanks, Takashi