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 X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2CD3FC433E0 for ; Thu, 7 Jan 2021 16:21:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D2A1A2339E for ; Thu, 7 Jan 2021 16:21:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726514AbhAGQUo (ORCPT ); Thu, 7 Jan 2021 11:20:44 -0500 Received: from verein.lst.de ([213.95.11.211]:41219 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726294AbhAGQUo (ORCPT ); Thu, 7 Jan 2021 11:20:44 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id AF1D467373; Thu, 7 Jan 2021 17:20:00 +0100 (CET) Date: Thu, 7 Jan 2021 17:20:00 +0100 From: Christoph Hellwig To: Satya Tangirala Cc: Alexander Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe Subject: Re: [PATCH] fs: Fix freeze_bdev()/thaw_bdev() accounting of bd_fsfreeze_sb Message-ID: <20210107162000.GA2693@lst.de> References: <20201224044954.1349459-1-satyat@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201224044954.1349459-1-satyat@google.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Can someone pick this up? Maybe through Jens' block tree as that is where my commit this is fixing up came from. For reference: Reviewed-by: Christoph Hellwig On Thu, Dec 24, 2020 at 04:49:54AM +0000, Satya Tangirala wrote: > freeze/thaw_bdev() currently use bdev->bd_fsfreeze_count to infer > whether or not bdev->bd_fsfreeze_sb is valid (it's valid iff > bd_fsfreeze_count is non-zero). thaw_bdev() doesn't nullify > bd_fsfreeze_sb. > > But this means a freeze_bdev() call followed by a thaw_bdev() call can > leave bd_fsfreeze_sb with a non-null value, while bd_fsfreeze_count is > zero. If freeze_bdev() is called again, and this time > get_active_super() returns NULL (e.g. because the FS is unmounted), > we'll end up with bd_fsfreeze_count > 0, but bd_fsfreeze_sb is > *untouched* - it stays the same (now garbage) value. A subsequent > thaw_bdev() will decide that the bd_fsfreeze_sb value is legitimate > (since bd_fsfreeze_count > 0), and attempt to use it. > > Fix this by always setting bd_fsfreeze_sb to NULL when > bd_fsfreeze_count is successfully decremented to 0 in thaw_sb(). > Alternatively, we could set bd_fsfreeze_sb to whatever > get_active_super() returns in freeze_bdev() whenever bd_fsfreeze_count > is successfully incremented to 1 from 0 (which can be achieved cleanly > by moving the line currently setting bd_fsfreeze_sb to immediately > after the "sync:" label, but it might be a little too subtle/easily > overlooked in future). > > This fixes the currently panicking xfstests generic/085. > > Fixes: 040f04bd2e82 ("fs: simplify freeze_bdev/thaw_bdev") > Signed-off-by: Satya Tangirala > --- > fs/block_dev.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/block_dev.c b/fs/block_dev.c > index 9e56ee1f2652..12a811a9ae4b 100644 > --- a/fs/block_dev.c > +++ b/fs/block_dev.c > @@ -606,6 +606,8 @@ int thaw_bdev(struct block_device *bdev) > error = thaw_super(sb); > if (error) > bdev->bd_fsfreeze_count++; > + else > + bdev->bd_fsfreeze_sb = NULL; > out: > mutex_unlock(&bdev->bd_fsfreeze_mutex); > return error; > -- > 2.29.2.729.g45daf8777d-goog ---end quoted text---