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 074BEC7EE29 for ; Thu, 8 Jun 2023 18:16:57 +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=0f32YC11oxJpSvuuW1vHRzz9ShpJcoktKeIuy1iTB2U=; b=Ek1TOyDiKv5YQ6 YCx7O4m8Tok8mEq87grrEEz4i/0nMHkCvDsJVKbFdVP/am1vKwAWJeA1Zaz44T0rtOJE30SWq9lh5 ERrvEDc4zA4bZOsfK89Neat/VsdZ8tlFbeQWvQ80tZA1721BG5fUbD7ZYH8xzGee5l/7OnB5JCQQF 0eAWT6y34+oSChfWtaSdipy90nVsQrOcy+2QvbKdKyIh/o5ESTmIefgB2sIABDR9+NEXzKLiUxFHN igeFb76jRfYlGBIfojBFXk+mQF6Rd4HzBTzKNboslhkID8HUtxRiFEQmQtvdqGfuH4kTTxhNKIhnu WDsn3uliAwRdKTFBGU2w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1q7KBp-00A8sF-22; Thu, 08 Jun 2023 18:16:53 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1q7KBn-00A8qM-0F for kexec@lists.infradead.org; Thu, 08 Jun 2023 18:16:52 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 88DB865048; Thu, 8 Jun 2023 18:16:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D951CC433EF; Thu, 8 Jun 2023 18:16:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686248210; bh=0F5VKq0HkkvER9fIMap91gj7noH+t+ITf+G4dCasmLw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LOqVE9G/yqfBHoE40yBk4gZdvdwddzIxHZHs0q7JfIdOKbR5KqY1cznII0SwsqYCJ Xay/7aOXsTDxwkQ0S+zc3dQMWfiMCDHyfTm6NSF+RAkbTI38vWEd3ibHFmHi2tQKY0 CVdkZL9npzbY50SY1BPzSjK6G6pY6v6WoNH5bSNOsX1xRxLLOIYp9QZtq0uzZx0n6e cUFU9sqPp7GBNJSyDnizRjYBD3skd+0ROxvoszQKH+VvoIKHk4pMwyBNWOX+Phd1ri bjaL/CLHX+NEdjhsgPqhanvDQaKA6GNv5Gp/N1whuWVyqQ1dCLxIWG+MikAewEEaig d/oaQQ/JXUy0Q== Date: Thu, 8 Jun 2023 11:16:49 -0700 From: "Darrick J. Wong" To: Jan Kara Cc: Christoph Hellwig , Luis Chamberlain , 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: <20230608181649.GF72224@frogsfrogsfrogs> References: <20230508011717.4034511-1-mcgrof@kernel.org> <20230508011717.4034511-4-mcgrof@kernel.org> <20230522234200.GC11598@frogsfrogsfrogs> <20230525141430.slms7f2xkmesezy5@quack3> <20230608091130.bthttzsmdeeiagof@quack3> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230608091130.bthttzsmdeeiagof@quack3> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230608_111651_187338_0ACD7A24 X-CRM114-Status: GOOD ( 33.11 ) 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, Jun 08, 2023 at 11:11:30AM +0200, Jan Kara wrote: > On Wed 07-06-23 22:29:04, Christoph Hellwig wrote: > > 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. > > OK, I agree the wrappers could be confusing (they didn't confuse me but > when you spelled it out, I agree). > > > > 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.. > > Well, we need to somehow settle on how to deal with a race when both kernel > & userspace race to freeze the filesystem and make the result consistent > with the situation when the fs is already frozen by someone. I'll see what I can do about that. > > > 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. > > OK. I'm not too hung up on BIT() macro. > > Honza > -- > Jan Kara > SUSE Labs, CR _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec