From patchwork Mon Mar 21 11:21:46 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: GitHub issues - opened X-Patchwork-Id: 553497 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 alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 83D84C433F5 for ; Mon, 21 Mar 2022 11:22:40 +0000 (UTC) Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id BF60D170E; Mon, 21 Mar 2022 12:21:47 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz BF60D170E DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1647861757; bh=kBd5J8GmExW/nH/OyArd9xGZPncS1P4U0dsKzfBFdjU=; h=From:To:In-Reply-To:References:Subject:Date:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=RQgakshPdkZi4b0O5vC3c7K8JKIBbELq/6DVd3LK2/HlhcfN1+K0ogCYSS4zYxpiG kQAicLxZZ6n8Nttz8mdnVMisssE0QnjZfAo9HxBGhazuMD368ZUG6sNoyiKji/Lst6 j/HGy6kp4aW6WyG57TjA5OfdiZ8EqEDCzx9UfT58= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id 56789F801D8; Mon, 21 Mar 2022 12:21:47 +0100 (CET) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 07311F800FD; Mon, 21 Mar 2022 12:21:46 +0100 (CET) Received: from webhooks-bot.alsa-project.org (gate.perex.cz [77.48.224.242]) by alsa1.perex.cz (Postfix) with ESMTP id 6AE32F800FD for ; Mon, 21 Mar 2022 12:21:41 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 6AE32F800FD MIME-Version: 1.0 From: GitHub issues - opened To: alsa-devel@alsa-project.org In-Reply-To: <1647861701073087931-webhooks-bot@alsa-project.org> References: <1647861701073087931-webhooks-bot@alsa-project.org> Subject: Huge avail value caused by inconsistency between snd_pcm_multi_status() and snd_pcm_multi_hwptr_update() Message-Id: <20220321112146.07311F800FD@alsa1.perex.cz> Date: Mon, 21 Mar 2022 12:21:46 +0100 (CET) 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" alsa-project/alsa-lib issue #217 was opened from infmagic2047: ## Symptom Using the following configuration with plugin `type multi`, `snd_pcm_avail()` may return huge values. ``` pcm.combined { type multi; slaves.a.pcm "dmix:CARD=0"; slaves.a.channels 2; slaves.b.pcm "dmix:CARD=1"; slaves.b.channels 2; bindings.0.slave a; bindings.0.channel 0; bindings.1.slave a; bindings.1.channel 1; bindings.2.slave b; bindings.2.channel 0; bindings.3.slave b; bindings.3.channel 1; } ``` The problem still occurs even when I set both slaves to `dmix:CARD=0`, so use this to reproduce the issue if you don't have multiple output devices. It can be verified with `aplay --test-position -D plug:combined /dev/urandom`. The output looks like this: ``` Playing raw data '/dev/urandom' : Unsigned 8 bit, Rate 8000 Hz, Mono Suspicious buffer position (1 total): avail = 765611936652984468, delay = 2582, buffer = 2730 Suspicious buffer position (2 total): avail = 762797186885877738, delay = 2752, buffer = 2730 Suspicious buffer position (3 total): avail = 759982437118771178, delay = 2752, buffer = 2730 Suspicious buffer position (4 total): avail = 757167687351664448, delay = 2922, buffer = 2730 Suspicious buffer position (5 total): avail = 754352937584557888, delay = 2922, buffer = 2730 Suspicious buffer position (6 total): avail = 751538187817451158, delay = 3092, buffer = 2730 Suspicious buffer position (7 total): avail = 748723438050344598, delay = 3092, buffer = 2730 Suspicious buffer position (8 total): avail = 745908688283237868, delay = 3262, buffer = 2730 Suspicious buffer position (9 total): avail = 743093938516131308, delay = 3262, buffer = 2730 Suspicious buffer position (10 total): avail = 740279188749024578, delay = 3432, buffer = 2730 ``` I'm using alsa-lib-1.2.6.1 on Gentoo Linux, kernel version is 5.16.15. ## Cause For `type multi` plugins, `snd_pcm_multi_status()` returns the hwptr of its master_slave, while `snd_pcm_multi_hwptr_update()` sets the hwptr based on all slaves. They are inconsistent, and can lead to problems for plugins in upper levels. In this particular case, there is a `type rate` plugin on top of `type multi`. It requires the underlying hwptr to be monotonic, and may either read the hwptr directly (in `snd_pcm_rate_sync_hwptr()`) or use the value from status (in `snd_pcm_rate_status()`). The inconsistency can cause hwptr to decrease, breaking the code of `type rate`. ## Attempted solution I'm able to fix the problem with the following patch, and haven't run into any problems. I'm unfamiliar with the code though, so the patch may be inefficient or incorrect in some way. ``` ``` Issue URL : https://github.com/alsa-project/alsa-lib/issues/217 Repository URL: https://github.com/alsa-project/alsa-lib diff -uNar --no-dereference alsa-lib-1.2.6.1/src/pcm/pcm_multi.c alsa-lib-1.2.6.1-new/src/pcm/pcm_multi.c --- alsa-lib-1.2.6.1/src/pcm/pcm_multi.c 2021-12-09 21:17:59.000000000 +0800 +++ alsa-lib-1.2.6.1-new/src/pcm/pcm_multi.c 2022-03-21 16:20:32.096036522 +0800 @@ -388,11 +388,21 @@ return 0; } +static snd_pcm_sframes_t snd_pcm_multi_avail_update(snd_pcm_t *pcm); static int snd_pcm_multi_status(snd_pcm_t *pcm, snd_pcm_status_t *status) { snd_pcm_multi_t *multi = pcm->private_data; snd_pcm_t *slave = multi->slaves[multi->master_slave].pcm; - return snd_pcm_status(slave, status); + + int err = snd_pcm_status(slave, status); + if (err < 0) + return err; + snd_pcm_sframes_t avail = snd_pcm_multi_avail_update(pcm); + if (avail < 0) + return avail; + status->hw_ptr = *pcm->hw.ptr; + status->avail = avail; + return 0; } static snd_pcm_state_t snd_pcm_multi_state(snd_pcm_t *pcm)