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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id EA389C7EE23 for ; Thu, 8 Jun 2023 05:29:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=40AOio4Qo/W25wyqUlqVf8RAVYOAUMPFX08CXNlNdEA=; b=qI4kaLifvmP8Oh XNWR5/It0xukYuEOxK+Aoy5OZq3mneGsOmnZ1KrSprnwNvrBVNDZtxTJvk07p3xiS5YSf/igcKt6e piERwrVi0EmSTlEFCL7Y/Ge3slhhfVVcN1+X9t3j0fW6siKYlImoDpNOWYXsdHtUxUk1t3u6UYLKV bwVx5uJohuOik5STfU0isVs4A8jVWp0jIrhkM9iPMrLvoeYhXx4ExKsIkJjTgFpRcCnQ5twbQDOqt qey+EU9qzGt4iQ7PKJVTQxFioYNbNfLs1371roiGJmAsO5ZTzNL+05rSBW0iflboEaFQl+aDQ7NN6 Gloe55yDVaiy4aNbIMZQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1q78Cp-0089Eg-0q; Thu, 08 Jun 2023 05:29:07 +0000 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-Disposition: inline In-Reply-To: <20230525141430.slms7f2xkmesezy5@quack3> X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.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. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec