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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 8F80AC67790 for ; Fri, 27 Jul 2018 05:20:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3DCC620673 for ; Fri, 27 Jul 2018 05:20:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3DCC620673 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729372AbeG0Gkj (ORCPT ); Fri, 27 Jul 2018 02:40:39 -0400 Received: from mx2.suse.de ([195.135.220.15]:55658 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725838AbeG0Gkj (ORCPT ); Fri, 27 Jul 2018 02:40:39 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3A1EEAE84; Fri, 27 Jul 2018 05:20:31 +0000 (UTC) Date: Fri, 27 Jul 2018 07:20:30 +0200 Message-ID: From: Takashi Iwai To: "Dae R. Jeong" Cc: perex@perex.cz, alsa-devel@alsa-project.org, kt0755@gmail.com, syzkaller@googlegroups.com, bammanag@purdue.edu, linux-kernel@vger.kernel.org Subject: Re: BUG: soft lockup in snd_virmidi_output_trigger In-Reply-To: <20180727041322.GA13067@dragonet> References: <20180726055326.GA12625@dragonet> <20180727041322.GA13067@dragonet> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/26 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 27 Jul 2018 06:13:22 +0200, Dae R. Jeong wrote: > > I tested it and it worked. > Thanks a lot! Good to hear. Below is the final patch with a proper comment (and with syzbot reported-by, too) I'm going to queue to sound.git tree. thanks, Takashi -- 8< -- From: Takashi Iwai Subject: [PATCH v2] ALSA: virmidi: Fix too long output trigger loop The virmidi output trigger tries to parse the all available bytes and process sequencer events as much as possible. In a normal situation, this is supposed to be relatively short, but a program may give a huge buffer and it'll take a long time in a single spin lock, which may eventually lead to a soft lockup. This patch simply adds a workaround, a cond_resched() call in the loop if applicable. A better solution would be to move the event processor into a work, but let's put a duct-tape quickly at first. Reported-and-tested-by: Dae R. Jeong Reported-by: syzbot+e4c8abb920efa77bace9@syzkaller.appspotmail.com Cc: Signed-off-by: Takashi Iwai --- sound/core/seq/seq_virmidi.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c index 289ae6bb81d9..8ebbca554e99 100644 --- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -163,6 +163,7 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream, int count, res; unsigned char buf[32], *pbuf; unsigned long flags; + bool check_resched = !in_atomic(); if (up) { vmidi->trigger = 1; @@ -200,6 +201,15 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream, vmidi->event.type = SNDRV_SEQ_EVENT_NONE; } } + if (!check_resched) + continue; + /* do temporary unlock & cond_resched() for avoiding + * CPU soft lockup, which may happen via a write from + * a huge rawmidi buffer + */ + spin_unlock_irqrestore(&substream->runtime->lock, flags); + cond_resched(); + spin_lock_irqsave(&substream->runtime->lock, flags); } out: spin_unlock_irqrestore(&substream->runtime->lock, flags); -- 2.18.0