The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From cfb3c85a600c6aa25a2581b3c1c4db3460f14e46 Mon Sep 17 00:00:00 2001

From: Jeffle Xu jefflexu@linux.alibaba.com Date: Fri, 22 May 2020 12:18:44 +0800 Subject: [PATCH] ext4: fix partial cluster initialization when splitting extent

Fix the bug when calculating the physical block number of the first block in the split extent.

This bug will cause xfstests shared/298 failure on ext4 with bigalloc enabled occasionally. Ext4 error messages indicate that previously freed blocks are being freed again, and the following fsck will fail due to the inconsistency of block bitmap and bg descriptor.

The following is an example case:

1. First, Initialize a ext4 filesystem with cluster size '16K', block size '4K', in which case, one cluster contains four blocks.

2. Create one file (e.g., xxx.img) on this ext4 filesystem. Now the extent tree of this file is like:

... 36864:[0]4:220160 36868:[0]14332:145408 51200:[0]2:231424 ...

3. Then execute PUNCH_HOLE fallocate on this file. The hole range is like:

.. ext4_ext_remove_space: dev 254,16 ino 12 since 49506 end 49506 depth 1 ext4_ext_remove_space: dev 254,16 ino 12 since 49544 end 49546 depth 1 ext4_ext_remove_space: dev 254,16 ino 12 since 49605 end 49607 depth 1 ...

4. Then the extent tree of this file after punching is like

... 49507:[0]37:158047 49547:[0]58:158087 ...

5. Detailed procedure of punching hole [49544, 49546]

5.1. The block address space: ``` lblk ~49505 49506 49507~49543 49544~49546 49547~ ---------+------+-------------+----------------+-------- extent | hole | extent | hole | extent ---------+------+-------------+----------------+-------- pblk ~158045 158046 158047~158083 158084~158086 158087~ ```

5.2. The detailed layout of cluster 39521: ``` cluster 39521 <------------------------------->

hole extent <----------------------><--------

lblk 49544 49545 49546 49547 +-------+-------+-------+-------+ | | | | | +-------+-------+-------+-------+ pblk 158084 1580845 158086 158087 ```

5.3. The ftrace output when punching hole [49544, 49546]: - ext4_ext_remove_space (start 49544, end 49546) - ext4_ext_rm_leaf (start 49544, end 49546, last_extent [49507(158047), 40], partial [pclu 39522 lblk 0 state 2]) - ext4_remove_blocks (extent [49507(158047), 40], from 49544 to 49546, partial [pclu 39522 lblk 0 state 2] - ext4_free_blocks: (block 158084 count 4) - ext4_mballoc_free (extent 1/6753/1)

5.4. Ext4 error message in dmesg: EXT4-fs error (device vdb): mb_free_blocks:1457: group 1, block 158084:freeing already freed block (bit 6753); block bitmap corrupt. EXT4-fs error (device vdb): ext4_mb_generate_buddy:747: group 1, block bitmap and bg descriptor inconsistent: 19550 vs 19551 free clusters

In this case, the whole cluster 39521 is freed mistakenly when freeing pblock 158084~158086 (i.e., the first three blocks of this cluster), although pblock 158087 (the last remaining block of this cluster) has not been freed yet.

The root cause of this isuue is that, the pclu of the partial cluster is calculated mistakenly in ext4_ext_remove_space(). The correct partial_cluster.pclu (i.e., the cluster number of the first block in the next extent, that is, lblock 49597 (pblock 158086)) should be 39521 rather than 39522.

Fixes: f4226d9ea400 ("ext4: fix partial cluster initialization") Signed-off-by: Jeffle Xu jefflexu@linux.alibaba.com Reviewed-by: Eric Whitney enwlinux@gmail.com Cc: stable@kernel.org # v3.19+ Link: https://lore.kernel.org/r/1590121124-37096-1-git-send-email-jefflexu@linux.a... Signed-off-by: Theodore Ts'o tytso@mit.edu

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 7d088ff1e902..221f240eae60 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -2844,7 +2844,7 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start, * in use to avoid freeing it when removing blocks. */ if (sbi->s_cluster_ratio > 1) { - pblk = ext4_ext_pblock(ex) + end - ee_block + 2; + pblk = ext4_ext_pblock(ex) + end - ee_block + 1; partial.pclu = EXT4_B2C(sbi, pblk); partial.state = nofree; }