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Message-ID: <142a28f9-5954-47f6-9c0c-26f7c142dbc1@huawei.com> Date: Thu, 26 Sep 2024 16:28:54 +0800 From: Baokun Li <libaokun1@...wei.com> To: Jan Kara <jack@...e.cz>, Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com> CC: <tytso@....edu>, <stable@...r.kernel.org>, Andreas Dilger <adilger.kernel@...ger.ca>, Stéphane Graber <stgraber@...raber.org>, Christian Brauner <brauner@...nel.org>, <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>, Wesley Hershberger <wesley.hershberger@...onical.com>, Yang Erkun <yangerkun@...wei.com> Subject: Re: [PATCH 1/1] ext4: fix crash on BUG_ON in ext4_alloc_group_tables 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? Thanks, Baokun --- diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index e04eb08b9060..1f01a7632149 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -253,10 +253,12 @@ static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned int flexbg_size, /* Avoid allocating large 'groups' array if not needed */ last_group = o_group | (flex_gd->resize_bg - 1); if (n_group <= last_group) - flex_gd->resize_bg = 1 << fls(n_group - o_group + 1); + flex_gd->resize_bg = 1 << fls(n_group - o_group); else if (n_group - last_group < flex_gd->resize_bg) - flex_gd->resize_bg = 1 << max(fls(last_group - o_group + 1), + flex_gd->resize_bg = 1 << max(fls(last_group - o_group), fls(n_group - last_group)); flex_gd->groups = kmalloc_array(flex_gd->resize_bg, sizeof(struct ext4_new_group_data),
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