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Wed, 20 Nov 2019 16:39:55 +0100 (CET) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 6F5CBF8013D; Wed, 20 Nov 2019 16:39:54 +0100 (CET) Received: from esa2.mentor.iphmx.com (esa2.mentor.iphmx.com [68.232.141.98]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id D0BA5F800FF for ; Wed, 20 Nov 2019 16:39:50 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz D0BA5F800FF IronPort-SDR: 2EKDaGg3m7wl7aoFuzlGEbgQncHOHckHdWPO7drhEmJ6iIBSjNp2E8HmBkOGwuT5kWZDxDxbGt Ivfg77xACMS7CWAzEM2TMBcW5US/b3kepVq+txcJFjFm6eT5J9EniRacyekI6XUGZHuVJt3OP7 t7jRPI/M9S1Gl/hx29c9NrWTtMwnUtnMiZPRE/+pRrBpt/weptE6QibuG/3o2nFkOToH7B+mZo Wg4eiROE7oJSOk7oZShXF/7gi6jo3b8NtxAT2jZ60HdgwOPyQ5v7NKoHSfGP99xfuqFg6YiEKC sUk= X-IronPort-AV: E=Sophos;i="5.69,222,1571731200"; d="scan'208";a="43292500" Received: from orw-gwy-02-in.mentorg.com ([192.94.38.167]) by esa2.mentor.iphmx.com with ESMTP; 20 Nov 2019 07:39:48 -0800 IronPort-SDR: NTLHtgw50zu5G6nn7et5/NosI5DsjGCJt4yYmrwXEgSLgwUDcIePX9YhYJ22olLVglU4VJZEES T9EsUAqlxbztKD4g7nINe5fTvRJHxyH0BTrgwYMobdWzTkh4MhQpxPuZyEB6YlfmcUCm3s9aoC QzY4SJGYvG9/MuPuHOhKayDpcPBMMEwZzvYychHTYS67SCgSqzSu8uhARozG7bgOtTVWufLn+W C2tr8stOM/CCeX/iE/5XNVJtDTm6L/bs+o2HQnhfOZiEXXYRehc3PsO5fNPJiw7tYCYPZToqjL sQs= From: Andrew Gabbasov To: 'Takashi Iwai' References: <20191120115856.4125-1-andrew_gabbasov@mentor.com> <20191120115856.4125-2-andrew_gabbasov@mentor.com> <20191120115856.4125-3-andrew_gabbasov@mentor.com> <20191120115856.4125-4-andrew_gabbasov@mentor.com> <20191120115856.4125-5-andrew_gabbasov@mentor.com> <20191120115856.4125-6-andrew_gabbasov@mentor.com> <20191120115856.4125-7-andrew_gabbasov@mentor.com> <000001d59fb6$4ca36aa0$e5ea3fe0$@mentor.com> In-Reply-To: Date: Wed, 20 Nov 2019 18:39:00 +0300 Organization: Mentor Graphics Corporation Message-ID: <000101d59fb8$a288a280$e799e780$@mentor.com> MIME-Version: 1.0 X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQHVn7ezhCAU3Kkkmk2hDkJrcybUyqeUMFOA Content-Language: en-us X-Originating-IP: [137.202.0.90] X-ClientProxiedBy: SVR-IES-MBX-03.mgc.mentorg.com (139.181.222.3) To svr-ies-mbx-02.mgc.mentorg.com (139.181.222.2) Cc: Timo Wischer , alsa-devel@alsa-project.org, Takashi Iwai , linux-kernel@vger.kernel.org Subject: Re: [alsa-devel] [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer instead of jiffies X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" Hello Takashi, > -----Original Message----- > From: Takashi Iwai [mailto:tiwai@suse.de] > Sent: Wednesday, November 20, 2019 6:32 PM > To: Gabbasov, Andrew > Cc: alsa-devel@alsa-project.org; linux-kernel@vger.kernel.org; Jaroslav > Kysela; Takashi Iwai; Timo Wischer > Subject: Re: [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer > instead of jiffies > > On Wed, 20 Nov 2019 16:21:36 +0100, > Andrew Gabbasov wrote: > > > > Hello Takashi, > > > > > -----Original Message----- > > > From: Takashi Iwai [mailto:tiwai@suse.de] > > > Sent: Wednesday, November 20, 2019 5:34 PM > > > To: Gabbasov, Andrew > > > Cc: alsa-devel@alsa-project.org; linux-kernel@vger.kernel.org; Jaroslav > > > Kysela; Takashi Iwai; Timo Wischer > > > Subject: Re: [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer > > > instead of jiffies > > > > > > On Wed, 20 Nov 2019 12:58:55 +0100, > > > Andrew Gabbasov wrote: > > > > +/* call in loopback->cable_lock */ > > > > +static int loopback_snd_timer_open(struct loopback_pcm *dpcm) > > > > +{ > > > > + int err = 0; > > > > + struct snd_timer_id tid = { > > > > + .dev_class = SNDRV_TIMER_CLASS_PCM, > > > > + .dev_sclass = SNDRV_TIMER_SCLASS_APPLICATION, > > > > + }; > > > > + struct snd_timer_instance *timeri; > > > > + struct loopback_cable *cable = dpcm->cable; > > > > + > > > > + spin_lock_irq(&cable->lock); > > > > + > > > > + /* check if timer was already opened. It is only opened once > > > > + * per playback and capture subdevice (aka cable). > > > > + */ > > > > + if (cable->snd_timer.instance) > > > > + goto unlock; > > > > + > > > > + err = loopback_parse_timer_id(dpcm->loopback->timer_source, > &tid); > > > > + if (err < 0) { > > > > + pcm_err(dpcm->substream->pcm, > > > > + "Parsing timer source \'%s\' failed with %d", > > > > + dpcm->loopback->timer_source, err); > > > > + goto unlock; > > > > + } > > > > + > > > > + cable->snd_timer.stream = dpcm->substream->stream; > > > > + cable->snd_timer.id = tid; > > > > + > > > > + timeri = snd_timer_instance_new(dpcm->loopback->card->id); > > > > + if (!timeri) { > > > > + err = -ENOMEM; > > > > + goto unlock; > > > > + } > > > > + /* The callback has to be called from another tasklet. If > > > > + * SNDRV_TIMER_IFLG_FAST is specified it will be called from > the > > > > + * snd_pcm_period_elapsed() call of the selected sound card. > > > > + * snd_pcm_period_elapsed() helds > snd_pcm_stream_lock_irqsave(). > > > > + * Due to our callback loopback_snd_timer_function() also > calls > > > > + * snd_pcm_period_elapsed() which calls > > > snd_pcm_stream_lock_irqsave(). > > > > + * This would end up in a dead lock. > > > > + */ > > > > + timeri->flags |= SNDRV_TIMER_IFLG_AUTO; > > > > + timeri->callback = loopback_snd_timer_function; > > > > + timeri->callback_data = (void *)cable; > > > > + timeri->ccallback = loopback_snd_timer_event; > > > > + > > > > + /* snd_timer_close() and snd_timer_open() should not be called > with > > > > + * locked spinlock because both functions can block on a > mutex. The > > > > + * mutex loopback->cable_lock is kept locked. Therefore > > > snd_timer_open() > > > > + * cannot be called a second time by the other device of the > same > > > cable. > > > > + * Therefore the following issue cannot happen: > > > > + * [proc1] Call loopback_timer_open() -> > > > > + * Unlock cable->lock for snd_timer_close/open() call > > > > + * [proc2] Call loopback_timer_open() -> snd_timer_open(), > > > > + * snd_timer_start() > > > > + * [proc1] Call snd_timer_open() and overwrite running timer > > > > + * instance > > > > + */ > > > > + spin_unlock_irq(&cable->lock); > > > > + err = snd_timer_open(timeri, &cable->snd_timer.id, current- > >pid); > > > > + if (err < 0) { > > > > + pcm_err(dpcm->substream->pcm, > > > > + "snd_timer_open (%d,%d,%d) failed with %d", > > > > + cable->snd_timer.id.card, > > > > + cable->snd_timer.id.device, > > > > + cable->snd_timer.id.subdevice, > > > > + err); > > > > + snd_timer_instance_free(timeri); > > > > + return err; > > > > + } > > > > + spin_lock_irq(&cable->lock); > > > > + > > > > + cable->snd_timer.instance = timeri; > > > > + > > > > + /* initialise a tasklet used for draining */ > > > > + tasklet_init(&cable->snd_timer.event_tasklet, > > > > + loopback_snd_timer_tasklet, (unsigned > long)timeri); > > > > > > This has to be set before snd_timer_open(). The callback might be > > > called immediately after snd_timer_open(). > > > > This tasklet is used/scheduled only in ccallback (not regular tick > > callback), > > and only for SNDRV_TIMER_EVENT_MSTOP event. Can this event really happen > > immediately after snd_timer_open()? > > Why not? The master timer can be stopped at any time, even between > these two lines. > > Beware that there are fuzzer programs that can trigger such racy > things, and you're adding the code to the target that is actively > slapped by them :) OK, got it. I'll move this initialization to before snd_timer_open() in the next update together with the fixes for the other issues you will find in this version. Thanks! Best regards, Andrew _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org https://mailman.alsa-project.org/mailman/listinfo/alsa-devel