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Tue, 6 Feb 2024 12:05:07 +0000 (UTC) X-Farcaster-Flow-ID: c9cfb521-cea1-4196-a5b8-62dd92c7f18e Received: from EX19D001UWB002.ant.amazon.com (10.13.138.54) by EX19MTAUWC002.ant.amazon.com (10.250.64.143) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Tue, 6 Feb 2024 12:05:07 +0000 Received: from EX19MTAUWA001.ant.amazon.com (10.250.64.204) by EX19D001UWB002.ant.amazon.com (10.13.138.54) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Tue, 6 Feb 2024 12:05:06 +0000 Received: from dev-dsk-mheyne-1b-c1362c4d.eu-west-1.amazon.com (10.15.57.183) by mail-relay.amazon.com (10.250.64.204) with Microsoft SMTP Server id 15.2.1118.40 via Frontend Transport; Tue, 6 Feb 2024 12:05:06 +0000 Received: by dev-dsk-mheyne-1b-c1362c4d.eu-west-1.amazon.com (Postfix, from userid 5466572) id 436D196C; Tue, 6 Feb 2024 12:05:06 +0000 (UTC) From: Maximilian Heyne To: CC: , Maximilian Heyne , Theodore Ts'o , Andreas Dilger , , Subject: [PATCH] ext4: fix corruption during on-line resize Date: Tue, 6 Feb 2024 12:05:04 +0000 Message-ID: <20240206120504.122870-1-mheyne@amazon.de> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 We observed a corruption during on-line resize of a file system that is larger than 16 TiB with 4k block size. With having more then 2^32 blocks resize_inode is turned off by default by mke2fs. The issue can be reproduced on a smaller file system for convenience by explicitly turning off resize_inode. An on-line resize across an 8 GiB boundary (the size of a meta block group in this setup) then leads to a corruption: dev=/dev/ # should be >= 16 GiB mkdir -p /corruption /sbin/mke2fs -t ext4 -b 4096 -O ^resize_inode $dev $((2 * 2**21 - 2**15)) mount -t ext4 $dev /corruption dd if=/dev/zero bs=4096 of=/corruption/test count=$((2*2**21 - 4*2**15)) sha1sum /corruption/test # 79d2658b39dcfd77274e435b0934028adafaab11 /corruption/test /sbin/resize2fs $dev $((2*2**21)) # drop page cache to force reload the block from disk echo 1 > /proc/sys/vm/drop_caches sha1sum /corruption/test # 3c2abc63cbf1a94c9e6977e0fbd72cd832c4d5c3 /corruption/test 2^21 = 2^15*2^6 equals 8 GiB whereof 2^15 is the number of blocks per block group and 2^6 are the number of block groups that make a meta block group. The last checksum might be different depending on how the file is laid out across the physical blocks. The actual corruption occurs at physical block 63*2^15 = 2064384 which would be the location of the backup of the meta block group's block descriptor. During the on-line resize the file system will be converted to meta_bg starting at s_first_meta_bg which is 2 in the example - meaning all block groups after 16 GiB. However, in ext4_flex_group_add we might add block groups that are not part of the first meta block group yet. In the reproducer we achieved this by substracting the size of a whole block group from the point where the meta block group would start. This must be considered when updating the backup block group descriptors to follow the non-meta_bg layout. The fix is to add a test whether the group to add is already part of the meta block group or not. Signed-off-by: Maximilian Heyne --- fs/ext4/resize.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 4d4a5a32e310..3433e83bb7a3 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1602,7 +1602,9 @@ static int ext4_flex_group_add(struct super_block *sb, int gdb_num = group / EXT4_DESC_PER_BLOCK(sb); int gdb_num_end = ((group + flex_gd->count - 1) / EXT4_DESC_PER_BLOCK(sb)); - int meta_bg = ext4_has_feature_meta_bg(sb); + unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb); + int meta_bg = ext4_has_feature_meta_bg(sb) && + metagroup >= le32_to_cpu(es->s_first_meta_bg); sector_t padding_blocks = meta_bg ? 0 : sbi->s_sbh->b_blocknr - ext4_group_first_block_no(sb, 0);