From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1F4412746D; Fri, 27 Sep 2024 01:43:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727401405; cv=none; b=aMsGFiHnuaHqAFfQs2CRBOb/Pv0+kuhl8wvONFLrLAhfZVDRok6m4gxz+B08zAd5CfN/E6+JSj/HUNJgCldiCY7g3gTgELDz7kg8MGp3Y5g1syJoNL1P9kolDnRWD+TEtw2u/Kqbyv4MMYuJMCy1Zt6NM3/FMNNtr+tVdn/8848= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727401405; c=relaxed/simple; bh=eThHgiFZLCQUTtc9xrFLaZUNnQjcwKmNmd28LqBUrx4=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=bbCX2/CcUj6BUKFZn95nV1g0SYbxhJ1wWLzX28f3JWAFeh+Ar75oudE7Oc0eiku2cXcCVhebxj+Ga5pj6M2CJgsBli5Jh82kJ/ut1RKV6UQMcwDqm7HSoEzeZ/q0n4b0WciCQxLzmYhpbxxsgw6WWZr91KdwqlPG4h9Ps2DMC54= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.17]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4XFCrd12pxz2DcZj; Fri, 27 Sep 2024 09:42:25 +0800 (CST) Received: from dggpeml100021.china.huawei.com (unknown [7.185.36.148]) by mail.maildlp.com (Postfix) with ESMTPS id 9118C1A0188; Fri, 27 Sep 2024 09:43:14 +0800 (CST) Received: from [127.0.0.1] (10.174.177.174) by dggpeml100021.china.huawei.com (7.185.36.148) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Fri, 27 Sep 2024 09:43:13 +0800 Message-ID: Date: Fri, 27 Sep 2024 09:43:13 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] ext4: fix crash on BUG_ON in ext4_alloc_group_tables To: Eric Sandeen CC: Jan Kara , Alexander Mikhalitsyn , , , Andreas Dilger , =?UTF-8?Q?St=C3=A9phane_Graber?= , Christian Brauner , , , , Wesley Hershberger , Yang Erkun , Baokun Li References: <20240925143325.518508-1-aleksandr.mikhalitsyn@canonical.com> <20240925143325.518508-2-aleksandr.mikhalitsyn@canonical.com> <20240925155706.zad2euxxuq7h6uja@quack3> <142a28f9-5954-47f6-9c0c-26f7c142dbc1@huawei.com> Content-Language: en-US From: Baokun Li In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpeml100021.china.huawei.com (7.185.36.148) On 2024/9/27 0:04, Eric Sandeen wrote: > On 9/26/24 3:28 AM, Baokun Li wrote: >> On 2024/9/25 23:57, Jan Kara wrote: >>> On Wed 25-09-24 16:33:24, Alexander Mikhalitsyn wrote: >>>> [   33.882936] EXT4-fs (dm-5): mounted filesystem 8aaf41b2-6ac0-4fa8-b92b-77d10e1d16ca r/w with ordered data mode. Quota mode: none. >>>> [   33.888365] EXT4-fs (dm-5): resizing filesystem from 7168 to 786432 blocks >>>> [   33.888740] ------------[ cut here ]------------ >>>> [   33.888742] kernel BUG at fs/ext4/resize.c:324! >>> Ah, I was staring at this for a while before I understood what's going on >>> (it would be great to explain this in the changelog BTW).  As far as I >>> understand commit 665d3e0af4d3 ("ext4: reduce unnecessary memory allocation >>> in alloc_flex_gd()") can actually make flex_gd->resize_bg larger than >>> flexbg_size (for example when ogroup = flexbg_size, ngroup = 2*flexbg_size >>> - 1) which then confuses things. I think that was not really intended and >>> instead of fixing up ext4_alloc_group_tables() we should really change >>> the logic in alloc_flex_gd() to make sure flex_gd->resize_bg never exceeds >>> flexbg size. Baokun? >>> >>>                                 Honza >> Hi Honza, >> >> Your analysis is absolutely correct. It's a bug! >> Thank you for locating this issue！ >> An extra 1 should not be added when calculating resize_bg in alloc_flex_gd(). >> >> >> Hi Aleksandr, >> >> Could you help test if the following changes work? >> > I just got an internal bug report for this as well, and I can also confirm that > the patch fixes my testcase, thanks! Feel free to add: > > Tested-by: Eric Sandeen > > I had been trying to debug this and it felt like an off by one but I didn't get > to a solution in time. ;) > > Can you explain what the 2 cases under > > /* Avoid allocating large 'groups' array if not needed */ > > are doing? I *think* the first 'if' is trying not to over-allocate for the last > batch of block groups that get added during a resize. What is the "else if" case > doing? > > Thanks, > -Eric > The ext4 online resize started out by allocating the memory needed for an entire flexible block group regardless of the number of block groups to be added. This led to a warning being triggered in the mm module when the userland set a very large flexbg_size (perhaps they wanted to put all the group metadata in the head of the disk), allocating more memory than the MAX_ORDER size. Commit 5d1935ac02ca5a ("ext4: avoid online resizing failures due to oversized flex bg") fixes this problem with resize_bg. Normally, when online resizing, we may not need to allocate the memory required for an entire flexible block group. So if o_group and n_group are in the same flexible block group or if o_group and n_group are in neighbouring flexible block groups, we check if less memory can be allocated. This is what was done in commit 665d3e0af4d3 ("ext4: reduce unnecessary memory allocation in alloc_flex_gd()"). Regards, Baokun