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 D2358C77B7F for ; Tue, 16 May 2023 15:17:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233695AbjEPPR2 (ORCPT ); Tue, 16 May 2023 11:17:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233778AbjEPPRY (ORCPT ); Tue, 16 May 2023 11:17:24 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 84E3C7D8E; Tue, 16 May 2023 08:17:20 -0700 (PDT) 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 1B55963B3A; Tue, 16 May 2023 15:17:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71041C433D2; Tue, 16 May 2023 15:17:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684250239; bh=zbsLxnAMj2vSIfOTUoVRyfsNlOWW5Uqw9nion1XeX4E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PMTpX/YIRwsa4A8MO42slLD90eYpwk5Grd8dbmfPivPpPaa1JOWehAz+POdgblVEh D2laHfSTr4zpFVohDVcUfQfbV2iXxVg2/qSgRoENMhBp4K6MQciHSqd9P5f+bXTsYn gDugDHX7qYxEug0WIvsmZsSQo42q4vGEUBe/KagYb8Gq8ZADtQ0aUARE/frffW64xP tGfTPg9hxILttqTIwg99VYf4MXvfWPAuuuC4osf00WezPA37h8Tp/z7rW55J+VR938 qE4WkuZyjG/1nZkz5l+EhlqVV/Oju2SjjDvgJB5Y8YHOWbAEGauCF63DmsD44zDIno dg/3E/HgJg8rQ== Date: Tue, 16 May 2023 08:17:18 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: Luis Chamberlain , hch@infradead.org, sandeen@sandeen.net, song@kernel.org, rafael@kernel.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, jack@suse.cz, 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 6/6] fs: add automatic kernel fs freeze / thaw and remove kthread freezing Message-ID: <20230516151718.GP858815@frogsfrogsfrogs> References: <20230508011717.4034511-1-mcgrof@kernel.org> <20230508011717.4034511-7-mcgrof@kernel.org> <20230509012013.GD2651828@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230509012013.GD2651828@dread.disaster.area> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 09, 2023 at 11:20:13AM +1000, Dave Chinner wrote: > On Sun, May 07, 2023 at 06:17:17PM -0700, Luis Chamberlain wrote: > > Add support to automatically handle freezing and thawing filesystems > > during the kernel's suspend/resume cycle. > > > > This is needed so that we properly really stop IO in flight without > > races after userspace has been frozen. Without this we rely on > > kthread freezing and its semantics are loose and error prone. > > For instance, even though a kthread may use try_to_freeze() and end > > up being frozen we have no way of being sure that everything that > > has been spawned asynchronously from it (such as timers) have also > > been stopped as well. > > > > A long term advantage of also adding filesystem freeze / thawing > > supporting during suspend / hibernation is that long term we may > > be able to eventually drop the kernel's thread freezing completely > > as it was originally added to stop disk IO in flight as we hibernate > > or suspend. > > > > This does not remove the superfluous freezer calls on all filesystems. > > Each filesystem must remove all the kthread freezer stuff and peg > > the fs_type flags as supporting auto-freezing with the FS_AUTOFREEZE > > flag. > > > > Subsequent patches remove the kthread freezer usage from each > > filesystem, one at a time to make all this work bisectable. > > Once all filesystems remove the usage of the kthread freezer we > > can remove the FS_AUTOFREEZE flag. > > > > Reviewed-by: Jan Kara > > Signed-off-by: Luis Chamberlain > > --- > > fs/super.c | 50 ++++++++++++++++++++++++++++++++++++++++++ > > include/linux/fs.h | 14 ++++++++++++ > > kernel/power/process.c | 15 ++++++++++++- > > 3 files changed, 78 insertions(+), 1 deletion(-) > > ..... > > > diff --git a/kernel/power/process.c b/kernel/power/process.c > > index cae81a87cc91..7ca7688f0b5d 100644 > > --- a/kernel/power/process.c > > +++ b/kernel/power/process.c > > @@ -140,6 +140,16 @@ int freeze_processes(void) > > > > BUG_ON(in_atomic()); > > > > + pr_info("Freezing filesystems ... "); > > + error = iterate_supers_reverse_excl(fs_suspend_freeze_sb, NULL); > > + if (error) { > > + pr_cont("failed\n"); > > + iterate_supers_excl(fs_suspend_thaw_sb, NULL); > > + thaw_processes(); > > + return error; > > That looks wrong. i.e. if the sb iteration fails to freeze a > filesystem (for whatever reason) then every userspace frozen > filesystem will be thawed by this call, right? i.e. it will thaw > more than just the filesystems frozen by the suspend freeze > iteration before it failed. > > Don't we only want to thaw the superblocks we froze before the > failure occurred? i.e. the "undo" iteration needs to start from the > last superblock we successfully froze and then only walk to the tail > of the list we started from? I think fs_suspend_thaw_sb calls thaw_super(..., false), which will not undo a userspace freeze. So strictly speaking the answer to your question is (AFAICT) "no it won't" That said, I read this and also had a raised-eyebrow moment -- we shouldn't (un?)touch superblocks that fs_suspend_freeze_sb didn't touch in the first place. I wonder if we should be using that NULL parameter to keep track of the last super that fs_suspend_freeze_sb didn't fail on? --D > > + } > > + pr_cont("done.\n"); > > + > > /* > > * Now that the whole userspace is frozen we need to disable > > * the OOM killer to disallow any further interference with > > @@ -149,8 +159,10 @@ int freeze_processes(void) > > if (!error && !oom_killer_disable(msecs_to_jiffies(freeze_timeout_msecs))) > > error = -EBUSY; > > > > - if (error) > > + if (error) { > > + iterate_supers_excl(fs_suspend_thaw_sb, NULL); > > thaw_processes(); > > + } > > Does this also have the same problem? i.e. if fs_suspend_freeze_sb() > skips over superblocks that are already userspace frozen without any > error, then this will incorrectly thaw those userspace frozen > filesystems. > > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com