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Fri, 15 Oct 2021 09:39:10 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 1FE90F8016C Authentication-Results: alsa1.perex.cz; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="oj51HIkl"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="n55k6ECZ" Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id D33DC21A64; Fri, 15 Oct 2021 07:39:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1634283549; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=olUjLJNS3fOuL0i9/OYwvQaN8GuL6EwBRWO7zYexHW8=; b=oj51HIkl500rl6EIAe+8j9/mwtjuHYj5RC3y074CqaUILqgLhCqVhW1mkafLPQBvSeSGY9 N/h7A8W1nYo8dxyRSiITED7powR8KpEh7vT6ombQVsd+tE9m1GzE5iLqwZ3lOEdDpJUwdB lwdMVQotzwvcHXnfUm5CrnejCrdIVIk= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1634283549; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=olUjLJNS3fOuL0i9/OYwvQaN8GuL6EwBRWO7zYexHW8=; b=n55k6ECZ1kSS1C0b59SV7gXz+NMbvs4ZrXU+QrX8qSTsiwxV846PieN37fIuMff3R3dYdb aOO6bgIzOFjQFNCg== Received: from alsa1.suse.de (alsa1.suse.de [10.160.4.42]) by relay2.suse.de (Postfix) with ESMTP id 2C198A3B84; Fri, 15 Oct 2021 07:39:09 +0000 (UTC) Date: Fri, 15 Oct 2021 09:39:09 +0200 Message-ID: From: Takashi Iwai To: Sameer Pujar Subject: Re: [RFC PATCH v3 05/13] ASoC: soc-pcm: align BE 'atomicity' with that of the FE In-Reply-To: <2847a6d1-d97f-4161-c8b6-03672cf6645c@nvidia.com> References: <20211013143050.244444-1-pierre-louis.bossart@linux.intel.com> <20211013143050.244444-6-pierre-louis.bossart@linux.intel.com> <2847a6d1-d97f-4161-c8b6-03672cf6645c@nvidia.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 Cc: alsa-devel@alsa-project.org, Kuninori Morimoto , open list , Takashi Iwai , Pierre-Louis Bossart , Liam Girdwood , vkoul@kernel.org, broonie@kernel.org, Gyeongtaek Lee , Peter Ujfalusi 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: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" On Fri, 15 Oct 2021 08:24:41 +0200, Sameer Pujar wrote: > > > > On 10/13/2021 8:00 PM, Pierre-Louis Bossart wrote: > > Since the flow for DPCM is based on taking a lock for the FE first, we > > need to make sure during the connection between a BE and an FE that > > they both use the same 'atomicity', otherwise we may sleep in atomic > > context. > > > > If the FE is nonatomic, this patch forces the BE to be nonatomic as > > well. That should have no negative impact since the BE 'inherits' the > > FE properties. > > > > However, if the FE is atomic and the BE is not, then the configuration > > is flagged as invalid. > > In normal PCM, atomicity seems to apply only for trigger(). Other > callbacks like prepare, hw_params are executed in non-atomic > context. So when 'nonatomic' flag is false, still it is possible to > sleep in a prepare or hw_param callback and this is true for FE as > well. So I am not sure if atomicity is applicable as a whole even for > FE. > > At this point it does not cause serious problems, but with subsequent > patches (especially when patch 7/13 is picked) I see failures. Please > refer to patch 7/13 thread for more details. > > > I am wondering if it is possible to only use locks internally for DPCM > state management and decouple BE callbacks from this, like normal PCMs > do? Actually the patch looks like an overkill by adding the FE stream lock at every loop, and this caused the problem, AFAIU. Basically we need to protect the link addition / deletion while the list traversal (there is a need for protection of BE vs BE access race, but that's a different code path). For the normal cases, it seems already protected by card->pcm_mutex, but the problem is the FE trigger case. It was attempted by dpcm_lock, but that failed because it couldn't be applied properly there. That said, what we'd need is only: - Drop dpcm_lock codes once - Put FE stream lock around dpcm_be_connect() and dpcm_be_disconnect() That should suffice for the race at trigger. The FE stream lock is already taken at trigger callback, and the rest list addition / deletion are called from different code paths without stream locks, so the explicit FE stream lock is needed there. In addition, a lock around dpcm_show_state() might be needed to be replaced with card->pcm_mutex, and we may need to revisit whether all other paths take card->pcm_mutex. Also, BE-vs-BE race can be protected by taking a BE lock inside dpcm_be_dai_trigger(). Takashi 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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1473BC433EF for ; Fri, 15 Oct 2021 07:39:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E186C61053 for ; Fri, 15 Oct 2021 07:39:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233694AbhJOHlR (ORCPT ); Fri, 15 Oct 2021 03:41:17 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:35992 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230471AbhJOHlQ (ORCPT ); Fri, 15 Oct 2021 03:41:16 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id D33DC21A64; Fri, 15 Oct 2021 07:39:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1634283549; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=olUjLJNS3fOuL0i9/OYwvQaN8GuL6EwBRWO7zYexHW8=; b=oj51HIkl500rl6EIAe+8j9/mwtjuHYj5RC3y074CqaUILqgLhCqVhW1mkafLPQBvSeSGY9 N/h7A8W1nYo8dxyRSiITED7powR8KpEh7vT6ombQVsd+tE9m1GzE5iLqwZ3lOEdDpJUwdB lwdMVQotzwvcHXnfUm5CrnejCrdIVIk= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1634283549; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=olUjLJNS3fOuL0i9/OYwvQaN8GuL6EwBRWO7zYexHW8=; b=n55k6ECZ1kSS1C0b59SV7gXz+NMbvs4ZrXU+QrX8qSTsiwxV846PieN37fIuMff3R3dYdb aOO6bgIzOFjQFNCg== Received: from alsa1.suse.de (alsa1.suse.de [10.160.4.42]) by relay2.suse.de (Postfix) with ESMTP id 2C198A3B84; Fri, 15 Oct 2021 07:39:09 +0000 (UTC) Date: Fri, 15 Oct 2021 09:39:09 +0200 Message-ID: From: Takashi Iwai To: Sameer Pujar Cc: Pierre-Louis Bossart , , , , Gyeongtaek Lee , Peter Ujfalusi , Kuninori Morimoto , Liam Girdwood , Jaroslav Kysela , Takashi Iwai , open list Subject: Re: [RFC PATCH v3 05/13] ASoC: soc-pcm: align BE 'atomicity' with that of the FE In-Reply-To: <2847a6d1-d97f-4161-c8b6-03672cf6645c@nvidia.com> References: <20211013143050.244444-1-pierre-louis.bossart@linux.intel.com> <20211013143050.244444-6-pierre-louis.bossart@linux.intel.com> <2847a6d1-d97f-4161-c8b6-03672cf6645c@nvidia.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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 15 Oct 2021 08:24:41 +0200, Sameer Pujar wrote: > > > > On 10/13/2021 8:00 PM, Pierre-Louis Bossart wrote: > > Since the flow for DPCM is based on taking a lock for the FE first, we > > need to make sure during the connection between a BE and an FE that > > they both use the same 'atomicity', otherwise we may sleep in atomic > > context. > > > > If the FE is nonatomic, this patch forces the BE to be nonatomic as > > well. That should have no negative impact since the BE 'inherits' the > > FE properties. > > > > However, if the FE is atomic and the BE is not, then the configuration > > is flagged as invalid. > > In normal PCM, atomicity seems to apply only for trigger(). Other > callbacks like prepare, hw_params are executed in non-atomic > context. So when 'nonatomic' flag is false, still it is possible to > sleep in a prepare or hw_param callback and this is true for FE as > well. So I am not sure if atomicity is applicable as a whole even for > FE. > > At this point it does not cause serious problems, but with subsequent > patches (especially when patch 7/13 is picked) I see failures. Please > refer to patch 7/13 thread for more details. > > > I am wondering if it is possible to only use locks internally for DPCM > state management and decouple BE callbacks from this, like normal PCMs > do? Actually the patch looks like an overkill by adding the FE stream lock at every loop, and this caused the problem, AFAIU. Basically we need to protect the link addition / deletion while the list traversal (there is a need for protection of BE vs BE access race, but that's a different code path). For the normal cases, it seems already protected by card->pcm_mutex, but the problem is the FE trigger case. It was attempted by dpcm_lock, but that failed because it couldn't be applied properly there. That said, what we'd need is only: - Drop dpcm_lock codes once - Put FE stream lock around dpcm_be_connect() and dpcm_be_disconnect() That should suffice for the race at trigger. The FE stream lock is already taken at trigger callback, and the rest list addition / deletion are called from different code paths without stream locks, so the explicit FE stream lock is needed there. In addition, a lock around dpcm_show_state() might be needed to be replaced with card->pcm_mutex, and we may need to revisit whether all other paths take card->pcm_mutex. Also, BE-vs-BE race can be protected by taking a BE lock inside dpcm_be_dai_trigger(). Takashi