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=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 47FC3C433FE for ; Fri, 11 Dec 2020 18:45:31 +0000 (UTC) Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6957323F37 for ; Fri, 11 Dec 2020 18:45:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6957323F37 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=alsa-devel-bounces@alsa-project.org Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id CE5F4173F; Fri, 11 Dec 2020 19:44:36 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz CE5F4173F DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1607712326; bh=oOy8p/YDAT7sYJv2Moo0iFWw3AP5DzR7W+FORCfLK+w=; h=Date:From:To:Subject:In-Reply-To:References:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=UxA+lxBDXiKJl8Ks+Pn8xd5PdgDicbyJSfvMOJWINCjcWrDuO/7lf9YKhMPXY1Nzh HSia1mQQu0Lx/l3nuh/0hjhlL1N1gyGtPCK8yUkkUbXMtMIyVgrlB+Jqyu6NguEmbB TgLbGYHYBV66k33B2JvEbyGgDRdt03zkt0dedBLE= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id 14430F801D8; Fri, 11 Dec 2020 19:44:36 +0100 (CET) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 87577F8020D; Fri, 11 Dec 2020 19:44:34 +0100 (CET) Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id 85777F8014E for ; Fri, 11 Dec 2020 19:44:19 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 85777F8014E X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A7565AC94; Fri, 11 Dec 2020 18:44:18 +0000 (UTC) Date: Fri, 11 Dec 2020 19:44:18 +0100 Message-ID: From: Takashi Iwai To: Jaroslav Kysela Subject: Re: [PATCH] alsactl: Skip restore during the lock In-Reply-To: References: <20201211083804.800-1-tiwai@suse.de> 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/25.3 (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 Cc: ALSA development X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" On Fri, 11 Dec 2020 18:56:56 +0100, Jaroslav Kysela wrote: > > Dne 11. 12. 20 v 18:37 Takashi Iwai napsal(a): > > On Fri, 11 Dec 2020 18:23:03 +0100, > > Jaroslav Kysela wrote: > >> > >> Dne 11. 12. 20 v 18:06 Takashi Iwai napsal(a): > >>> On Fri, 11 Dec 2020 17:59:05 +0100, > >>> Takashi Iwai wrote: > >>>> > >>>> On Fri, 11 Dec 2020 17:45:45 +0100, > >>>> Jaroslav Kysela wrote: > >>>>> > >>>>> Dne 11. 12. 20 v 9:38 Takashi Iwai napsal(a): > >>>>>> Currently alsactl-restore tries to initialize the device when an error > >>>>>> is found for restore action. But this isn't the right behavior in the > >>>>>> case where the lock is held; it implies that another alsactl is > >>>>>> running concurrently, hence you shouldn't initialize the card at the > >>>>>> same time. The situation is found easily when two alsactls get > >>>>>> started by both udev and systemd (note that those two invocations are > >>>>>> the designed behavior, see /usr/lib/udev/rules.d/78-sound-cards.rules > >>>>>> for details). > >>>>>> > >>>>>> This patch changes load_state() not to handle the initialization if > >>>>>> the locking fails. > >>>>> > >>>>> The operation should serialize in this case (there's limit of 10 seconds which > >>>>> should be enough to finish the initialization). The state_lock() function > >>>>> should return -EBUSY when the file is locked (and I'm fine to change the > >>>>> behaviour from 'init' to 'skip' for this lock state). > >>>>> > >>>>> It seems that -EEXIST is returned when the lock file exists, but the > >>>>> open(file, O_CREAT|O_EXCL, 0644) caller has not enough priviledges to access > >>>>> this file when another user owns the file. > >>>>> > >>>>> But alsactl from /lib/udev/rules.d/90-alsa-restore.rules and > >>>>> /lib/systemd/system/alsa-restore.service should be run as root, right? > >>>> > >>>> Yes, it should be root. > >>>> > >>>> I also wondered how EEXIST comes, too. Maybe it's also the race > >>>> between the first open(O_RDWR) and the second > >>>> open(O_RDWR|O_CREAT|O_EXCL)? If so, it'd be better to go back again > >>>> to the normal open(O_RDWR)? > >>> > >>> ... something like below > >>> > >>> > >>> diff --git a/alsactl/lock.c b/alsactl/lock.c > >>> index 4a485392b3bd..c1c30f0c5eee 100644 > >>> --- a/alsactl/lock.c > >>> +++ b/alsactl/lock.c > >>> @@ -64,6 +64,9 @@ static int state_lock_(const char *file, int lock, int timeout, int _fd) > >>> if (errno == EBUSY || errno == EAGAIN) { > >>> sleep(1); > >>> timeout--; > >>> + } if (errno == EEXIST){ > >>> + /* race at creating a lock, try again */ > >>> + continue; > >>> } else { > >>> err = -errno; > >>> goto out; > >> > >> If we don't use the sleep call and the timeout counter, there's endless CPU > >> busy loop when the root creates the lock file and user wants to access it for > >> example. It's better to add EEXIST to the previous errno condition. > > > > The timeout is decreased in the while condition. > > It seems not correct. It decreases the wait time to half. My fault :-( > > What about this straight change: > > --- a/alsactl/lock.c > +++ b/alsactl/lock.c > @@ -63,11 +63,15 @@ static int state_lock_(const char *file, int lock, int > timeout, int _fd) > if (fd < 0) { > if (errno == EBUSY || errno == EAGAIN) { > sleep(1); > - timeout--; > - } else { > - err = -errno; > - goto out; > + continue; > } > + if (errno == EEXIST) { > + fd = open(nfile, O_RDWR); > + if (fd >= 0) > + break; > + } > + err = -errno; > + goto out; > } > } > } Yes, this should work. Shall I resubmit? I'd split to two, one to correct doubly timeout decreases and another to handle EEXIST. thanks, Takashi