From patchwork Tue Oct 27 13:52:42 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 311861 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20EEEC56202 for ; Tue, 27 Oct 2020 17:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC1CB21D42 for ; Tue, 27 Oct 2020 17:56:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603821398; bh=J4FfHhLDEh0Nlpe8vsWHG3Hw8kONUu6/CIsZCuXQOP8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Bx8fRB6cihTmOitR+Y9GvT4pvZZJBabZTMAiD7UYnUQwbI7aUaX8pCVNDtYD4XLi/ bMnrYvvixoA0rrWkVirYmUhZxbbXrGVnub7JD3RGcmW/44ytctsk6KBXfpz1bhGRGK /aAEtunVZtLfWQMKX57GLmp8S/p/9bgnf0rmlu5o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2901213AbgJ0OVQ (ORCPT ); Tue, 27 Oct 2020 10:21:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:45444 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2901199AbgJ0OVM (ORCPT ); Tue, 27 Oct 2020 10:21:12 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 93B56207BB; Tue, 27 Oct 2020 14:21:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603808472; bh=J4FfHhLDEh0Nlpe8vsWHG3Hw8kONUu6/CIsZCuXQOP8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=K1VnNYYwl8FUmQ4ytFvNekHXUOwb0djjrgJ0wxd+m7Gt8yJoqq2eIt5bI7WIQBYNX zfuVt4tbMh1QXO+VvDFnVgbWWOBVvk/O8nlrIMSgXzIkkdAOEyr9RDBncB/yUvo0yZ S0EMpMZbiVvaY0NqCMo/6MuHqjgZs4z1n5xQpapg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Pavel Machek , Takashi Iwai , Sasha Levin Subject: [PATCH 4.19 104/264] ALSA: seq: oss: Avoid mutex lock for a long-time ioctl Date: Tue, 27 Oct 2020 14:52:42 +0100 Message-Id: <20201027135435.574761712@linuxfoundation.org> X-Mailer: git-send-email 2.29.1 In-Reply-To: <20201027135430.632029009@linuxfoundation.org> References: <20201027135430.632029009@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Takashi Iwai [ Upstream commit 2759caad2600d503c3b0ed800e7e03d2cd7a4c05 ] Recently we applied a fix to cover the whole OSS sequencer ioctls with the mutex for dealing with the possible races. This works fine in general, but in theory, this may lead to unexpectedly long stall if an ioctl like SNDCTL_SEQ_SYNC is issued and an event with the far future timestamp was queued. For fixing such a potential stall, this patch changes the mutex lock applied conditionally excluding such an ioctl command. Also, change the mutex_lock() with the interruptible version for user to allow escaping from the big-hammer mutex. Fixes: 80982c7e834e ("ALSA: seq: oss: Serialize ioctls") Suggested-by: Pavel Machek Link: https://lore.kernel.org/r/20200922083856.28572-1-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Sasha Levin --- sound/core/seq/oss/seq_oss.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/sound/core/seq/oss/seq_oss.c b/sound/core/seq/oss/seq_oss.c index ed5bca0db3e73..f4a9d9972330b 100644 --- a/sound/core/seq/oss/seq_oss.c +++ b/sound/core/seq/oss/seq_oss.c @@ -187,9 +187,12 @@ odev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) if (snd_BUG_ON(!dp)) return -ENXIO; - mutex_lock(®ister_mutex); + if (cmd != SNDCTL_SEQ_SYNC && + mutex_lock_interruptible(®ister_mutex)) + return -ERESTARTSYS; rc = snd_seq_oss_ioctl(dp, cmd, arg); - mutex_unlock(®ister_mutex); + if (cmd != SNDCTL_SEQ_SYNC) + mutex_unlock(®ister_mutex); return rc; }