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 AEFBFC7EE23 for ; Thu, 8 Jun 2023 09:12:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233955AbjFHJLg (ORCPT ); Thu, 8 Jun 2023 05:11:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233222AbjFHJLe (ORCPT ); Thu, 8 Jun 2023 05:11:34 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2D40E7; Thu, 8 Jun 2023 02:11:32 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 7E7AB21A0C; Thu, 8 Jun 2023 09:11:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1686215491; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Od9uQp8BPquVZWVULhzN4uIvhtmuiD3iT/Esw6XDZfE=; b=zI/R2a7qogDApLYGMtJPQPsAFnhtCjWN36ew59aELXtTTukycHqmVhEI/O+N7Em0YLW6yL tXNQH19K+VT3iSoUb6dFMVDP1kRqek2NS1qcyjAIryR72QSnnqITI6HaGOB3KuVdWBJTbA 3m1wkJmzDt/ZvYggvusEW1Q4eMauE8I= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1686215491; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Od9uQp8BPquVZWVULhzN4uIvhtmuiD3iT/Esw6XDZfE=; b=aQS/z1F/B0PhcL7Le5/KreM7Fiaot+tUlAF4L1yNx5rf3nvK1niRiGlng+olEpfqtK6P/8 ZqjVRLD0SVJKEfAw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 6A5F713480; Thu, 8 Jun 2023 09:11:31 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id oIvpGUObgWSsZgAAMHmgww (envelope-from ); Thu, 08 Jun 2023 09:11:31 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 0210BA0749; Thu, 8 Jun 2023 11:11:30 +0200 (CEST) Date: Thu, 8 Jun 2023 11:11:30 +0200 From: Jan Kara To: Christoph Hellwig Cc: Jan Kara , "Darrick J. Wong" , 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: <20230608091130.bthttzsmdeeiagof@quack3> 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: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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. > > 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