6.6-stable review patch. If anyone has any objections, please let me know.
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From: Uladzislau Rezki (Sony) urezki@gmail.com
commit 7fa3e7d114abc9cc71cc35d768e116641074ddb4 upstream.
When performing a read-modify-write(RMW) operation, any modification to a buffered block must cause the entire buffer to be marked dirty.
Marking only a subrange as dirty is incorrect because the underlying device block size(ubs) defines the minimum read/write granularity. A lower device can perform I/O only on regions which are fully aligned and sized to ubs.
This change ensures that write-back operations always occur in full ubs-sized chunks, matching the intended emulation semantics of the EBS target.
As for user space visible impact, submitting sub-ubs and misaligned I/O for devices which are tuned to ubs sizes only, will reject such requests, therefore it can lead to losing data. Example:
1) Create a 8K nvme device in qemu by adding
-device nvme,drive=drv0,serial=foo,logical_block_size=8192,physical_block_size=8192
2) Setup dm-ebs to emulate 512B to 8K mapping
urezki@pc638:~/bin$ cat dmsetup.sh
lower=/dev/nvme0n1 len=$(blockdev --getsz "$lower")
echo "0 $len ebs $lower 0 1 16" | dmsetup create nvme-8k urezki@pc638:~/bin$
offset 0, ebs=1 and ubs=16(in sectors).
3) Create an ext4 filesystem(default 4K block size)
urezki@pc638:~/bin$ sudo mkfs.ext4 -F /dev/dm-0 mke2fs 1.47.0 (5-Feb-2023) Discarding device blocks: done Creating filesystem with 2072576 4k blocks and 518144 inodes Filesystem UUID: bd0b6ca6-0506-4e31-86da-8d22c9d50b63 Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632
Allocating group tables: done Writing inode tables: done Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: mkfs.ext4: Input/output error while writing out and closing file system urezki@pc638:~/bin$ dmesg
<snip> [ 1618.875449] buffer_io_error: 1028 callbacks suppressed [ 1618.875456] Buffer I/O error on dev dm-0, logical block 0, lost async page write [ 1618.875527] Buffer I/O error on dev dm-0, logical block 1, lost async page write [ 1618.875602] Buffer I/O error on dev dm-0, logical block 2, lost async page write [ 1618.875620] Buffer I/O error on dev dm-0, logical block 3, lost async page write [ 1618.875639] Buffer I/O error on dev dm-0, logical block 4, lost async page write [ 1618.894316] Buffer I/O error on dev dm-0, logical block 5, lost async page write [ 1618.894358] Buffer I/O error on dev dm-0, logical block 6, lost async page write [ 1618.894380] Buffer I/O error on dev dm-0, logical block 7, lost async page write [ 1618.894405] Buffer I/O error on dev dm-0, logical block 8, lost async page write [ 1618.894427] Buffer I/O error on dev dm-0, logical block 9, lost async page write <snip>
Many I/O errors because the lower 8K device rejects sub-ubs/misaligned requests.
with a patch:
urezki@pc638:~/bin$ sudo mkfs.ext4 -F /dev/dm-0 mke2fs 1.47.0 (5-Feb-2023) Discarding device blocks: done Creating filesystem with 2072576 4k blocks and 518144 inodes Filesystem UUID: 9b54f44f-ef55-4bd4-9e40-c8b775a616ac Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632
Allocating group tables: done Writing inode tables: done Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: done
urezki@pc638:~/bin$ sudo mount /dev/dm-0 /mnt/ urezki@pc638:~/bin$ ls -al /mnt/ total 24 drwxr-xr-x 3 root root 4096 Oct 17 15:13 . drwxr-xr-x 19 root root 4096 Jul 10 19:42 .. drwx------ 2 root root 16384 Oct 17 15:13 lost+found urezki@pc638:~/bin$
After this change: mkfs completes; mount succeeds.
Signed-off-by: Uladzislau Rezki (Sony) urezki@gmail.com Signed-off-by: Mikulas Patocka mpatocka@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/md/dm-ebs-target.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/md/dm-ebs-target.c +++ b/drivers/md/dm-ebs-target.c @@ -103,7 +103,7 @@ static int __ebs_rw_bvec(struct ebs_c *e } else { flush_dcache_page(bv->bv_page); memcpy(ba, pa, cur_len); - dm_bufio_mark_partial_buffer_dirty(b, buf_off, buf_off + cur_len); + dm_bufio_mark_buffer_dirty(b); }
dm_bufio_release(b);