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 62CABC7EE2E for ; Thu, 8 Jun 2023 05:29:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234313AbjFHF3T (ORCPT ); Thu, 8 Jun 2023 01:29:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37672 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231320AbjFHF3S (ORCPT ); Thu, 8 Jun 2023 01:29:18 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 528B719BB; Wed, 7 Jun 2023 22:29:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=AuoFXc6mC0CchCsTVGZxzFlsH6pVBxlEu3dUOFHvvfQ=; b=Syo8qVTQpUGvrpjzKiLhGW4olW sJuNZOHW1JESoIpqG4kgoklwg3rwUAFASf7B6oBHY5dODAeP78HHiYpWmm8fNpb2AylunV5ggx2nN bSkP1HbE6kIDxyPuD5LPCsuvGdGbFuRVJWHopON+ddKYPDSuIqlVTWeivflo87mpRvQXouGK0DlzL 0JIVL5XtASvtBxvljSTzt1cSr2ykwQbgEQ8PcbGpA3OUsb+yQP3VVq65/sDTX85I8iFU+WoAmVGxj vJaMn5xsEK/APxX4HcwaqnHAGlXeRB5D8IkNkiTf1onh9i+Z2yWqjW5r6FltWRt6Dgkk7e4MLuJwz Bo9HgZpQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.96 #2 (Red Hat Linux)) id 1q78Cm-0089EH-1Y; Thu, 08 Jun 2023 05:29:04 +0000 Date: Wed, 7 Jun 2023 22:29:04 -0700 From: Christoph Hellwig To: Jan Kara Cc: "Darrick J. Wong" , Luis Chamberlain , hch@infradead.org, sandeen@sandeen.net, song@kernel.org, rafael@kernel.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, jikos@kernel.org, bvanassche@acm.org, ebiederm@xmission.com, mchehab@kernel.org, keescook@chromium.org, p.raghav@samsung.com, da.gomez@samsung.com, linux-fsdevel@vger.kernel.org, kernel@tuxforce.de, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/6] fs: distinguish between user initiated freeze and kernel initiated freeze Message-ID: References: <20230508011717.4034511-1-mcgrof@kernel.org> <20230508011717.4034511-4-mcgrof@kernel.org> <20230522234200.GC11598@frogsfrogsfrogs> <20230525141430.slms7f2xkmesezy5@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230525141430.slms7f2xkmesezy5@quack3> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, May 25, 2023 at 04:14:30PM +0200, Jan Kara wrote: > Yes, this is exactly how I'd imagine it. Thanks for writing the patch! > > I'd just note that this would need rebasing on top of Luis' patches 1 and > 2. Also: I'd not do that for now. 1 needs a lot more work, and 2 seems rather questionable. > Now the only remaining issue with the code is that the two different > holders can be attempting to freeze the filesystem at once and in that case > one of them has to wait for the other one instead of returning -EBUSY as > would happen currently. This can happen because we temporarily drop > s_umount in freeze_super() due to lock ordering issues. I think we could > do something like: > > if (!sb_unfrozen(sb)) { > up_write(&sb->s_umount); > wait_var_event(&sb->s_writers.frozen, > sb_unfrozen(sb) || sb_frozen(sb)); > down_write(&sb->s_umount); > goto retry; > } > > and then sprinkle wake_up_var(&sb->s_writers.frozen) at appropriate places > in freeze_super(). Let's do that separately as a follow on.. > > BTW, when reading this code, I've spotted attached cleanup opportunity but > I'll queue that separately so that is JFYI. > > > +#define FREEZE_HOLDER_USERSPACE (1U << 1) /* userspace froze fs */ > > +#define FREEZE_HOLDER_KERNEL (1U << 2) /* kernel froze fs */ > > Why not start from 1U << 0? And bonus points for using BIT() macro :). BIT() is a nasty thing and actually makes code harder to read. And it doesn't interact very well with the __bitwise annotation that might actually be useful here.