On Fri, May 18, 2018 at 02:43:02PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
>
> Jun Wu at Facebook reported that an internal service was seeing a return
> value of 1 from ftruncate() on Btrfs when compression is enabled. This
> is coming from the NEED_TRUNCATE_BLOCK return value from
> btrfs_truncate_inode_items().
>
> btrfs_truncate() uses two variables for error handling, ret and err (if
> this sounds familiar, it's because btrfs_truncate_inode_items() does
> something similar). When btrfs_truncate_inode_items() returns non-zero,
> we set err to the return value, but we don't reset it to zero in the
> successful NEED_TRUNCATE_BLOCK case. We only have err because we don't
> want to mask an error if we call btrfs_update_inode() and
> btrfs_end_transaction(), so let's make that its own scoped return
> variable and use ret everywhere else.
To expand on this, this is bad because userspace that checks for a
non-zero return value will think the truncate failed even though it
succeeded, and we also end up not creating an inotify event for the
truncate.
> Fixes: ddfae63cc8e0 ("btrfs: move btrfs_truncate_block out of trans handle")
> Reported-by: Jun Wu <quark@xxxxxx>
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> ---
> This is based on Linus' master rather than my orphan ENOSPC fixes
> because I think we want to get this in for v4.17 and stable, and rebase
> my fixes on top of this.
>
> fs/btrfs/inode.c | 34 ++++++++++++++--------------------
> 1 file changed, 14 insertions(+), 20 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index d241285a0d2a..d4a47ae36ed8 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -9031,8 +9031,7 @@ static int btrfs_truncate(struct inode *inode, bool skip_writeback)
> struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> struct btrfs_root *root = BTRFS_I(inode)->root;
> struct btrfs_block_rsv *rsv;
> - int ret = 0;
> - int err = 0;
> + int ret;
> struct btrfs_trans_handle *trans;
> u64 mask = fs_info->sectorsize - 1;
> u64 min_size = btrfs_calc_trunc_metadata_size(fs_info, 1);
> @@ -9092,7 +9091,7 @@ static int btrfs_truncate(struct inode *inode, bool skip_writeback)
> */
> trans = btrfs_start_transaction(root, 2);
> if (IS_ERR(trans)) {
> - err = PTR_ERR(trans);
> + ret = PTR_ERR(trans);
> goto out;
> }
>
> @@ -9116,23 +9115,19 @@ static int btrfs_truncate(struct inode *inode, bool skip_writeback)
> inode->i_size,
> BTRFS_EXTENT_DATA_KEY);
> trans->block_rsv = &fs_info->trans_block_rsv;
> - if (ret != -ENOSPC && ret != -EAGAIN) {
> - err = ret;
> + if (ret != -ENOSPC && ret != -EAGAIN)
> break;
> - }
>
> ret = btrfs_update_inode(trans, root, inode);
> - if (ret) {
> - err = ret;
> + if (ret)
> break;
> - }
>
> btrfs_end_transaction(trans);
> btrfs_btree_balance_dirty(fs_info);
>
> trans = btrfs_start_transaction(root, 2);
> if (IS_ERR(trans)) {
> - ret = err = PTR_ERR(trans);
> + ret = PTR_ERR(trans);
> trans = NULL;
> break;
> }
> @@ -9168,26 +9163,25 @@ static int btrfs_truncate(struct inode *inode, bool skip_writeback)
> if (ret == 0 && inode->i_nlink > 0) {
> trans->block_rsv = root->orphan_block_rsv;
> ret = btrfs_orphan_del(trans, BTRFS_I(inode));
> - if (ret)
> - err = ret;
> }
>
> if (trans) {
> + int ret2;
> +
> trans->block_rsv = &fs_info->trans_block_rsv;
> - ret = btrfs_update_inode(trans, root, inode);
> - if (ret && !err)
> - err = ret;
> + ret2 = btrfs_update_inode(trans, root, inode);
> + if (ret2 && !ret)
> + ret = ret2;
>
> - ret = btrfs_end_transaction(trans);
> + ret2 = btrfs_end_transaction(trans);
> + if (ret2 && !ret)
> + ret = ret2;
> btrfs_btree_balance_dirty(fs_info);
> }
> out:
> btrfs_free_block_rsv(fs_info, rsv);
>
> - if (ret && !err)
> - err = ret;
> -
> - return err;
> + return ret;
> }
>
> /*
> --
> 2.17.0
>
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