From: Josh Triplett josh@joshtriplett.org

commit b1489186cc8391e0c1e342f9fbc3eedf6b944c61 upstream.

The in-kernel ext4 resize code doesn't support filesystem with the sparse_super2 feature. It fails with errors like this and doesn't finish the resize:

EXT4-fs (loop0): resizing filesystem from 16640 to 7864320 blocks EXT4-fs warning (device loop0): verify_reserved_gdb:760: reserved GDT 2 missing grp 1 (32770) EXT4-fs warning (device loop0): ext4_resize_fs:2111: error (-22) occurred during file system resize EXT4-fs (loop0): resized filesystem to 2097152

To reproduce: mkfs.ext4 -b 4096 -I 256 -J size=32 -E resize=$((256*1024*1024)) -O sparse_super2 ext4.img 65M truncate -s 30G ext4.img mount ext4.img /mnt python3 -c 'import fcntl, os, struct ; fd = os.open("/mnt", os.O_RDONLY | os.O_DIRECTORY) ; fcntl.ioctl(fd, 0x40086610, struct.pack("Q", 30 * 1024 * 1024 * 1024 // 4096), False) ; os.close(fd)' dmesg | tail e2fsck ext4.img

The userspace resize2fs tool has a check for this case: it checks if the filesystem has sparse_super2 set and if the kernel provides /sys/fs/ext4/features/sparse_super2. However, the former check requires manually reading and parsing the filesystem superblock.

Detect this case in ext4_resize_begin and error out early with a clear error message.

Signed-off-by: Josh Triplett josh@joshtriplett.org Link: https://lore.kernel.org/r/74b8ae78405270211943cd7393e65586c5faeed1.162309325... Signed-off-by: Theodore Ts'o tytso@mit.edu --- fs/ext4/resize.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 928700d57eb6..6513079c728b 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -74,6 +74,11 @@ int ext4_resize_begin(struct super_block *sb) return -EPERM; }

+ if (ext4_has_feature_sparse_super2(sb)) { + ext4_msg(sb, KERN_ERR, "Online resizing not supported with sparse_super2"); + return -EOPNOTSUPP; + } + if (test_and_set_bit_lock(EXT4_FLAGS_RESIZING, &EXT4_SB(sb)->s_ext4_flags)) ret = -EBUSY;