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 3EACFC76196 for ; Mon, 3 Apr 2023 14:21:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233132AbjDCOVN (ORCPT ); Mon, 3 Apr 2023 10:21:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233130AbjDCOVD (ORCPT ); Mon, 3 Apr 2023 10:21:03 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6FB6B31985 for ; Mon, 3 Apr 2023 07:20:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 085C5B81BB0 for ; Mon, 3 Apr 2023 14:20:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 778E1C433EF; Mon, 3 Apr 2023 14:20:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1680531609; bh=Q/0sdqO0FiJ7V7rS205kadL9fntsC5T3cXvcgQCejSk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sM6ushCpEWakE8ZfxejJWpAbaLMPJtd0bjDY9mDiYBycerxglPdd/FaeDIUNI+Tt6 j97Sh5byRx3x6dKNN5Xp5Sj6kQlJnPygNjaACy08Mcrjj7IZFkovfeKuHRE8fPc9SC EIcW6I2u197w3LjzPgOzPHN4yq8mKRGriEuzWa9o= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Alvin=20=C5=A0ipraga?= , Ruslan Bilovol , John Keeping Subject: [PATCH 5.4 044/104] usb: gadget: u_audio: dont let userspace block driver unbind Date: Mon, 3 Apr 2023 16:08:36 +0200 Message-Id: <20230403140406.122930071@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230403140403.549815164@linuxfoundation.org> References: <20230403140403.549815164@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Alvin Šipraga commit 6c67ed9ad9b83e453e808f9b31a931a20a25629b upstream. 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 Reviewed-by: Ruslan Bilovol Reviewed-by: John Keeping Link: https://lore.kernel.org/r/20230302163648.3349669-1-alvin@pqrs.dk Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/function/u_audio.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/usb/gadget/function/u_audio.c +++ b/drivers/usb/gadget/function/u_audio.c @@ -626,7 +626,7 @@ void g_audio_cleanup(struct g_audio *g_a uac = g_audio->uac; card = uac->card; if (card) - snd_card_free(card); + snd_card_free_when_closed(card); kfree(uac->p_prm.ureq); kfree(uac->c_prm.ureq);