From nobody Wed Sep 3 05:52:26 2025 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 B6596C38A2D for ; Mon, 24 Oct 2022 12:17:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232983AbiJXMRE (ORCPT ); Mon, 24 Oct 2022 08:17:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233428AbiJXMPG (ORCPT ); Mon, 24 Oct 2022 08:15:06 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C042880531; Mon, 24 Oct 2022 04:56:00 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 03AEA612E6; Mon, 24 Oct 2022 11:55:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14FA6C433D6; Mon, 24 Oct 2022 11:55:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666612555; bh=3WzImQnkbjG9/1b+5+7IqgwI/RK4Rp5ceJx3SH2/qCg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JhYGwyK2KzLbYK2vh6bfBV5xZ/bSWBfLRA3EpqZv1YNn0nyzu9SKEpuTUv8+mWTT/ Ghv/U5cOCZs9oQkr6f7nWo2SvtMynXl2cYdtChBpVqC6C1ym5BB9WGbVRoe84Ykp3l emueMsbYgtm6SCy1qUj1fJpTmzaLVCoI+BRMSayI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Takashi Iwai Subject: [PATCH 4.19 032/229] ALSA: oss: Fix potential deadlock at unregistration Date: Mon, 24 Oct 2022 13:29:11 +0200 Message-Id: <20221024113000.158366599@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024112959.085534368@linuxfoundation.org> References: <20221024112959.085534368@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Takashi Iwai commit 97d917879d7f92df09c3f21fd54609a8bcd654b2 upstream. We took sound_oss_mutex around the calls of unregister_sound_special() at unregistering OSS devices. This may, however, lead to a deadlock, because we manage the card release via the card's device object, and the release may happen at unregister_sound_special() call -- which will take sound_oss_mutex again in turn. Although the deadlock might be fixed by relaxing the rawmidi mutex in the previous commit, it's safer to move unregister_sound_special() calls themselves out of the sound_oss_mutex, too. The call is race-safe as the function has a spinlock protection by itself. Link: https://lore.kernel.org/r/CAB7eexJP7w1B0mVgDF0dQ+gWor7UdkiwPczmL7pn91= xx8xpzOA@mail.gmail.com Cc: Link: https://lore.kernel.org/r/20221011070147.7611-2-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/sound_oss.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) --- a/sound/core/sound_oss.c +++ b/sound/core/sound_oss.c @@ -177,7 +177,6 @@ int snd_unregister_oss_device(int type, mutex_unlock(&sound_oss_mutex); return -ENOENT; } - unregister_sound_special(minor); switch (SNDRV_MINOR_OSS_DEVICE(minor)) { case SNDRV_MINOR_OSS_PCM: track2 =3D SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_AUDIO); @@ -189,12 +188,18 @@ int snd_unregister_oss_device(int type, track2 =3D SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_DMMIDI1); break; } - if (track2 >=3D 0) { - unregister_sound_special(track2); + if (track2 >=3D 0) snd_oss_minors[track2] =3D NULL; - } snd_oss_minors[minor] =3D NULL; mutex_unlock(&sound_oss_mutex); + + /* call unregister_sound_special() outside sound_oss_mutex; + * otherwise may deadlock, as it can trigger the release of a card + */ + unregister_sound_special(minor); + if (track2 >=3D 0) + unregister_sound_special(track2); + kfree(mptr); return 0; }