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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54B9CC433F5 for ; Sat, 29 Jan 2022 03:33:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352296AbiA2Ddf (ORCPT ); Fri, 28 Jan 2022 22:33:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50854 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241053AbiA2Ddc (ORCPT ); Fri, 28 Jan 2022 22:33:32 -0500 Received: from mail-wr1-x431.google.com (mail-wr1-x431.google.com [IPv6:2a00:1450:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F799C061714 for ; Fri, 28 Jan 2022 19:33:32 -0800 (PST) Received: by mail-wr1-x431.google.com with SMTP id c23so14417794wrb.5 for ; Fri, 28 Jan 2022 19:33:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:subject:to:cc:message-id:date:user-agent:mime-version :content-transfer-encoding:content-language; bh=MEEV8WH7gcIBaywuZqpSloW8+fQPmSsXYorwBGkwcEQ=; b=ft1K6ec+bpsSUrO6sHzilNhZI5D7ygOV6cUs23pfaPUJ86HDBgX0unZVVHu1tlpSzV S3HLok9V9mqEFkQpws5xw3ogn4wQonCdzOjENUWOUKy8jo4+t3fYvLRvRDxuVO+D/A8n uVVH1VpoDrgOPq8e6nNviJBhGUMnUUFf351smOMUpH42GpfGrQUlo0HiNEt2nPCdDija Nq1cTeDQUAxClEhhGfdNvCub+wDMVFSBMW86P6wTCiyT0VBQQyrZ/86VMrYpRGJ/eYAN FSNbmr2PQVAZT2m7sVIM3lcR8LHGZiXTF1Eg54+4IXZ+i/y0eIvKSj1+PNMrNzT/eDp0 Bv9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:subject:to:cc:message-id:date:user-agent :mime-version:content-transfer-encoding:content-language; bh=MEEV8WH7gcIBaywuZqpSloW8+fQPmSsXYorwBGkwcEQ=; b=qV5bbmOlw5qPl7I8S8gH79zffgbrRabGbmgrte/1jDpYiCmantQ5MiDz3Y4lbCItKT rffOMNfOpgvFtwMiYN1m75IwT8kFyiEwH8De+uVEo5Nflq4JNIjnmNqZxgPoXtJkCn8N y8+g0b50V31P60GILrqppvAMIhkt9R1UhEUhDNa4MYvWHP2U+iCUECqXetTFcBnZWmtP WNgyqOQv3N3xmHEVHDhV5hkckt4xo6CCsiuSt3HAJVMf9lMfqNM4mYM4dc6iqS9qdWx1 NPheYCVCCFSNsnp1EY55AlBRn2MYT7oCyBNdNre25nuiMfbgxg/mMhogbmRQsXQeDV/H QlDA== X-Gm-Message-State: AOAM530gPm0OUVX5IFlnnCF/pJNDsc7GAuLGjU/h6291cyuKLuK97i6U 17OPLOfl5PXpqEuv4tL8qAl700Uvy2k= X-Google-Smtp-Source: ABdhPJyiMDc7MH6tbWAjV3Be75ZoFQZE5hbcKQdm0LjQKmgM7IzYGTiitEr0vIiW8lRjpb0lPUKvKQ== X-Received: by 2002:a5d:494b:: with SMTP id r11mr9289806wrs.626.1643427210591; Fri, 28 Jan 2022 19:33:30 -0800 (PST) Received: from [10.96.0.6] ([85.203.46.187]) by smtp.gmail.com with ESMTPSA id j19sm3551042wmq.17.2022.01.28.19.33.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Jan 2022 19:33:30 -0800 (PST) From: Jia-Ju Bai Subject: [BUG] ALSA: core: possible deadlock involving waiting and locking operations To: perex@perex.cz, tiwai@suse.com, broonie@kernel.org, o-takashi@sakamocchi.jp Cc: alsa-devel@alsa-project.org, linux-kernel Message-ID: <56766037-972e-9e5b-74c1-88633a72a77f@gmail.com> Date: Sat, 29 Jan 2022 11:33:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, My static analysis tool reports a possible deadlock in the sound driver in Linux 5.10: snd_card_disconnect_sync()   spin_lock_irq(&card->files_lock); --> Line 461 (Lock A)   wait_event_lock_irq(card->remove_sleep, ...); --> Line 462 (Wait X)   spin_unlock_irq(&card->files_lock); --> Line 465 (Unlock A) snd_hwdep_release()   mutex_lock(&hw->open_mutex); --> Line 152 (Lock B)   mutex_unlock(&hw->open_mutex); --> Line 157 (Unlock B)   snd_card_file_remove()     wake_up_all(&card->remove_sleep); --> Line 976 (Wake X) snd_hwdep_open()   mutex_lock(&hw->open_mutex); --> Line 95 (Lock B)   snd_card_file_add()     spin_lock(&card->files_lock); --> Line 932 (Lock A)     spin_unlock(&card->files_lock); --> Line 940 (Unlock A)   mutex_unlock(&hw->open_mutex); --> Line 139 (Unlock B) When snd_card_disconnect_sync() is executed, "Wait X" is performed by holding "Lock A". If snd_hwdep_open() is executed at this time, it holds "Lock B" and then waits for acquiring "Lock A". If snd_hwdep_release() is executed at this time, it waits for acquiring "Lock B", and thus "Wake X" cannot be performed to wake up "Wait X" in snd_card_disconnect_sync(), causing a possible deadlock. I am not quite sure whether this possible problem is real and how to fix it if it is real. Any feedback would be appreciated, thanks :) Best wishes, Jia-Ju Bai