From patchwork Thu Mar 2 16:36:47 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Alvin_=C5=A0ipraga?= X-Patchwork-Id: 658995 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 15754C7EE2F for ; Thu, 2 Mar 2023 16:38:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229563AbjCBQiW (ORCPT ); Thu, 2 Mar 2023 11:38:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbjCBQiU (ORCPT ); Thu, 2 Mar 2023 11:38:20 -0500 Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8388016899 for ; Thu, 2 Mar 2023 08:37:34 -0800 (PST) Received: by mail-ed1-x529.google.com with SMTP id s26so69801421edw.11 for ; Thu, 02 Mar 2023 08:37:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pqrs.dk; s=google; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=tfY1Ul1QnfuQtui+4Ej95F51iCd9NVPI2d94LXtRwmo=; b=bDoI/39/km5XuwmNOoWn9p3W5zwRXDGImrlqwgWO1zuWUu1uLGMwSch+pf0z7lOVEk 73JivL/5QyrKUaadxgCH/zBN/F+kuk2N5+pmDTVCqty5ou9Lp5ebIvJuY0sM6+2Ye5lX Ct4Fw8SaWySke/s2OpZJIlJv6gBiooF1l0PkA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=tfY1Ul1QnfuQtui+4Ej95F51iCd9NVPI2d94LXtRwmo=; b=E6KivDubmNlnlZb4pnReYTO/POiiLUTMrBIQOAM3pSYYTjMmzP/miXSLSUUtRe/XqH L6UjX1u7Pu8mCIZtsFc6TNmCYgNUqn+tmkZLRIJUDDD/wAFyBN10Ii2y/NPF8uOYdV1f AgKM8FaIbJ3HXYB2v9Etl0QSp0fizKPATNheS6FAnfUhejgQO4OHaLubK9sw0vTcdwSI 5uArvBWANBMQqhr6v6p4z5YiMCqAMtkK1/0orVbf72pDwFAcRDcu/nrsEzQpV3ecOttk 3leXcju8zCUSHN8BTd3oxa9K+Ic2Q8Z1fLzx5DbkaiyLsRQMlDDrJ3Re9vctTNrvLqpI CdEQ== X-Gm-Message-State: AO0yUKUf3NlpYfttR+GgKRW/hcmYvbOUn4/qi35kxrdil9djMI3NDXt3 /zMqufYKRAzc0HF8RHkOtjEe7z6DOahJsKj+/dCx5w== X-Google-Smtp-Source: AK7set9auJrOCtINNaTDbetFrZVlHmp0QiBEME8aEHEdjzC6Rn02Ru1UVtQvJaLObY5/foEdxrwdfw== X-Received: by 2002:a17:906:6543:b0:8a9:e031:c4ae with SMTP id u3-20020a170906654300b008a9e031c4aemr10818449ejn.2.1677775047510; Thu, 02 Mar 2023 08:37:27 -0800 (PST) Received: from localhost.localdomain (80.71.142.18.ipv4.parknet.dk. [80.71.142.18]) by smtp.gmail.com with ESMTPSA id os6-20020a170906af6600b008f7f6943d1dsm7173547ejb.42.2023.03.02.08.37.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Mar 2023 08:37:27 -0800 (PST) From: =?utf-8?q?Alvin_=C5=A0ipraga?= To: Jaroslav Kysela , Takashi Iwai , Greg Kroah-Hartman , Yadi Brar , Jassi Brar , Felipe Balbi Cc: alsa-devel@alsa-project.org, =?utf-8?q?Alvin_=C5=A0ipraga?= , stable@vger.kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] usb: gadget: u_audio: don't let userspace block driver unbind Date: Thu, 2 Mar 2023 17:36:47 +0100 Message-Id: <20230302163648.3349669-1-alvin@pqrs.dk> X-Mailer: git-send-email 2.39.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org From: Alvin Šipraga In the unbind callback for f_uac1 and f_uac2, a call to snd_card_free() via g_audio_cleanup() will disconnect the card and then wait for all resources to be released, which happens when the refcount falls to zero. Since userspace can keep the refcount incremented by not closing the relevant file descriptor, the call to unbind may block indefinitely. This can cause a deadlock during reboot, as evidenced by the following blocked task observed on my machine: task:reboot state:D stack:0 pid:2827 ppid:569 flags:0x0000000c Call trace: __switch_to+0xc8/0x140 __schedule+0x2f0/0x7c0 schedule+0x60/0xd0 schedule_timeout+0x180/0x1d4 wait_for_completion+0x78/0x180 snd_card_free+0x90/0xa0 g_audio_cleanup+0x2c/0x64 afunc_unbind+0x28/0x60 ... kernel_restart+0x4c/0xac __do_sys_reboot+0xcc/0x1ec __arm64_sys_reboot+0x28/0x30 invoke_syscall+0x4c/0x110 ... The issue can also be observed by opening the card with arecord and then stopping the process through the shell before unbinding: # arecord -D hw:UAC2Gadget -f S32_LE -c 2 -r 48000 /dev/null Recording WAVE '/dev/null' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo ^Z[1]+ Stopped arecord -D hw:UAC2Gadget -f S32_LE -c 2 -r 48000 /dev/null # echo gadget.0 > /sys/bus/gadget/drivers/configfs-gadget/unbind (observe that the unbind command never finishes) Fix the problem by using snd_card_free_when_closed() instead, which will still disconnect the card as desired, but defer the task of freeing the resources to the core once userspace closes its file descriptor. Fixes: 132fcb460839 ("usb: gadget: Add Audio Class 2.0 Driver") Cc: stable@vger.kernel.org Signed-off-by: Alvin Šipraga --- drivers/usb/gadget/function/u_audio.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c index c1f62e91b012..4a42574b4a7f 100644 --- a/drivers/usb/gadget/function/u_audio.c +++ b/drivers/usb/gadget/function/u_audio.c @@ -1422,7 +1422,7 @@ void g_audio_cleanup(struct g_audio *g_audio) uac = g_audio->uac; card = uac->card; if (card) - snd_card_free(card); + snd_card_free_when_closed(card); kfree(uac->p_prm.reqs); kfree(uac->c_prm.reqs);