Commit 47b5d646 authored by Wang Xiaoguang's avatar Wang Xiaoguang Committed by David Sterba

btrfs: fix false enospc error when truncating heavily reflinked file

Below test script can reveal this bug:
    dd if=/dev/zero of=fs.img bs=$((1024*1024)) count=100
    dev=$(losetup --show -f fs.img)
    mkdir -p /mnt/mntpoint
    mkfs.btrfs  -f $dev
    mount $dev /mnt/mntpoint
    cd /mnt/mntpoint

    echo "workdir is: /mnt/mntpoint"
    blocksize=$((128 * 1024))
    dd if=/dev/zero of=testfile bs=$blocksize count=1
    sync
    count=$((17*1024*1024*1024/blocksize))
    echo "file size is:" $((count*blocksize))
    for ((i = 1; i <= $count; i++)); do
        dst_offset=$((blocksize * i))
        xfs_io -f -c "reflink testfile 0 $dst_offset $blocksize"\
                testfile > /dev/null
    done
    sync
    truncate --size 0 testfile

The last truncate operation will fail for ENOSPC reason, but indeed
it should not fail.

In btrfs_truncate(), we use a temporary block_rsv to do truncate
operation. With every btrfs_truncate_inode_items() call, we migrate space
to this block_rsv, but forget to cleanup previous reservation, which
will make this block_rsv's reserved bytes keep growing, and this reserved
space will only be released in the end of btrfs_truncate(), this metadata
leak will impact other's metadata reservation. In this case, it's
"btrfs_start_transaction(root, 2);" fails for enospc error, which make
this truncate operation fail.

Call btrfs_block_rsv_release() to fix this bug.
Signed-off-by: default avatarWang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 0bf70aeb
...@@ -9215,6 +9215,7 @@ static int btrfs_truncate(struct inode *inode) ...@@ -9215,6 +9215,7 @@ static int btrfs_truncate(struct inode *inode)
break; break;
} }
btrfs_block_rsv_release(fs_info, rsv, -1);
ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
rsv, min_size, 0); rsv, min_size, 0);
BUG_ON(ret); /* shouldn't happen */ BUG_ON(ret); /* shouldn't happen */
......
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