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 853F7C7EE23 for ; Mon, 12 Jun 2023 04:01:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231603AbjFLEBu (ORCPT ); Mon, 12 Jun 2023 00:01:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33756 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230436AbjFLEBt (ORCPT ); Mon, 12 Jun 2023 00:01:49 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDC41F3; Sun, 11 Jun 2023 21:01:48 -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=xaenqfQWcrt8tWNB36muhsuAFWAiB1Cw0mrXd/6ozhs=; b=hFyETY+oYsUZtG11PLJnEw7ZYu p2JXob13WXM2yyU16oeU+XARj2lFszgYIBN8pVhz6dH2pyByljza22w7Xire2GdD1NSA0FB4stkCn 0zSOyTDM5/dWagM/lFnfPqsgnB9hpFyYOs7saC5DopED9EsJuev8E2rTRENzQlWN5PotjAc4sf7gW OxJM5tSTNFF8c1l255fVz/u6kKkwGGnEcIma+4T56iQJWCw+qyA5isB1Ksctriej6oWoGeRA7sgL2 HOx+c3HGz6YXQZ/6p72gl9JYAjeg1SHWinRmJkER/2dfzYJeV44mcJLgJcVSe0FWHl5B+ATcE/+m9 0FInOqMg==; Received: from hch by bombadil.infradead.org with local (Exim 4.96 #2 (Red Hat Linux)) id 1q8YkW-002UPs-1y; Mon, 12 Jun 2023 04:01:48 +0000 Date: Sun, 11 Jun 2023 21:01:48 -0700 From: Christoph Hellwig To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, mcgrof@kernel.org, jack@suse.cz, hch@infradead.org, ruansy.fnst@fujitsu.com Subject: Re: [PATCH 2/3] fs: wait for partially frozen filesystems Message-ID: References: <168653971691.755178.4003354804404850534.stgit@frogsfrogsfrogs> <168653972832.755178.18389114450766371923.stgit@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <168653972832.755178.18389114450766371923.stgit@frogsfrogsfrogs> 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-xfs@vger.kernel.org On Sun, Jun 11, 2023 at 08:15:28PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong > > Jan Kara suggested that when one thread is in the middle of freezing a > filesystem, another thread trying to freeze the same fs but with a > different freeze_holder should wait until the freezer reaches either end > state (UNFROZEN or COMPLETE) instead of returning EBUSY immediately. > > Plumb in the extra coded needed to wait for the fs freezer to reach an > end state and try the freeze again. > > Signed-off-by: Darrick J. Wong > --- > fs/super.c | 27 +++++++++++++++++++++++++-- > 1 file changed, 25 insertions(+), 2 deletions(-) > > > diff --git a/fs/super.c b/fs/super.c > index 36adccecc828..151e0eeff2c2 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -1647,6 +1647,15 @@ static int freeze_frozen_super(struct super_block *sb, enum freeze_holder who) > return 0; > } > > +static void wait_for_partially_frozen(struct super_block *sb) > +{ > + up_write(&sb->s_umount); > + wait_var_event(&sb->s_writers.frozen, > + sb->s_writers.frozen == SB_UNFROZEN || > + sb->s_writers.frozen == SB_FREEZE_COMPLETE); > + down_write(&sb->s_umount); Does sb->s_writers.frozen need WRITE_ONCE/READ_ONCE treatment if we want to check it outside of s_umount? Or should we maybe just open code wait_var_event and only drop the lock after checking the variable? > if (sb->s_writers.frozen != SB_UNFROZEN) { > - deactivate_locked_super(sb); > - return -EBUSY; > + if (!try_again) { > + deactivate_locked_super(sb); > + return -EBUSY; > + } > + > + wait_for_partially_frozen(sb); > + try_again = false; > + goto retry; Can you throw in a comment on wait we're only waiting for a partial freeze one here?