On Thu, Jun 29, 2017 at 01:53:19PM -0400, Theodore Ts'o wrote:
> On Thu, Jun 29, 2017 at 09:57:27AM -0600, Ross Zwisler wrote:
> > On Thu, Jun 29, 2017 at 09:35:38AM -0600, Ross Zwisler wrote:
> > > Our validation team noticed that in some configurations mkfs.ext4 with the
> > > -D option creates a filesystem that can't be mounted:
>
> The -D option just means that we're doing the I/O using Direct I/O (as
> opposed to buffered I/O). It shouldn't make any difference to what
> gets written, so this very much smells like a bug in how /dev/pmem
> supports Direct I/O...
>
> > One more bit of info - this seems to be strongly tied to the size of the
> > block device. With a 32 GB block device it works fine, with 248 GB you get
> > overlap messages for groups 1 through 63, and with a 250 GB device you get
> > overlaps for groups 1 through 1999.
>
> This very much sounds like Direct I/O is just getting completely
> botched for the pmem device, and writes to a block group descriptor
> block is affecting the wrong place on the storage device.
This also reproduces with brd or loop as our block device:
# modprobe brd rd_size=$((1024*1024*248))
# mkfs.ext4 /dev/ram0 -F -D
mke2fs 1.43.3 (04-Sep-2016)
Discarding device blocks: done
Creating filesystem with 65011712 4k blocks and 16252928 inodes
Filesystem UUID: 1632baa4-7260-4cc1-9558-0cb3aa2f213e
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872
Allocating group tables: done
Writing inode tables: done
Creating journal (262144 blocks): done
Writing superblocks and filesystem accounting information: done
# mount /dev/ram0 /mnt
mount: wrong fs type, bad option, bad superblock on /dev/ram0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.
where dmesg says:
EXT4-fs (ram0): ext4_check_descriptors: Block bitmap for group 64 overlaps superblock
EXT4-fs (ram0): ext4_check_descriptors: Inode bitmap for group 64 overlaps superblock
EXT4-fs (ram0): ext4_check_descriptors: Inode table for group 64 overlaps superblock
EXT4-fs (ram0): ext4_check_descriptors: Block bitmap for group 65 overlaps superblock
EXT4-fs (ram0): ext4_check_descriptors: Inode bitmap for group 65 overlaps superblock
...
EXT4-fs (ram0): ext4_check_descriptors: Block bitmap for group 1983 overlaps superblock
EXT4-fs (ram0): ext4_check_descriptors: Inode bitmap for group 1983 overlaps superblock
EXT4-fs (ram0): ext4_check_descriptors: Inode table for group 1983 overlaps superblock
EXT4-fs (ram0): no journal found
or
# truncate -s 248G loop_fs
# losetup /dev/loop0 ./loop_fs
# mkfs.ext4 /dev/loop0 -F -D
mke2fs 1.43.3 (04-Sep-2016)
/dev/loop0 contains a ext4 file system
last mounted on Thu Jun 29 17:03:07 2017
Discarding device blocks: done
Creating filesystem with 65011712 4k blocks and 16252928 inodes
Filesystem UUID: 00912ac9-599a-4396-9ef3-a353bdec69ea
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872
Allocating group tables: done
Writing inode tables: done
Creating journal (262144 blocks): done
Writing superblocks and filesystem accounting information: done
# mount /dev/loop0 /tmp
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.
with similar messages.
- Ross
