Messages in this thread | | | From | Filipe Manana <> | Date | Mon, 20 Apr 2020 18:31:11 +0100 | Subject | Re: [PATCH] btrfs: Fix btrfs_block_group refcnt leak |
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On Mon, Apr 20, 2020 at 6:48 AM Xiyu Yang <xiyuyang19@fudan.edu.cn> wrote: > > btrfs_remove_block_group() invokes btrfs_lookup_block_group(), which > returns a local reference of the blcok group that contains the given > bytenr to "block_group" with increased refcount. > > When btrfs_remove_block_group() returns, "block_group" becomes invalid, > so the refcount should be decreased to keep refcount balanced. > > The reference counting issue happens in several exception handling paths > of btrfs_remove_block_group(). When those error scenarios occur such as > btrfs_alloc_path() returns NULL, the function forgets to decrease its > refcnt increased by btrfs_lookup_block_group() and will cause a refcnt > leak. > > Fix this issue by jumping to "out_put_group" label and calling > btrfs_put_block_group() when those error scenarios occur. > > Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn> > Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Seems correct to me. I would change the subject to something more clear like: "btrfs: fix block group leak after failure to remove it"
One more suggestion below.
> --- > fs/btrfs/block-group.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c > index 404e050ce8ee..d9f432bd3329 100644 > --- a/fs/btrfs/block-group.c > +++ b/fs/btrfs/block-group.c > @@ -916,7 +916,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > path = btrfs_alloc_path(); > if (!path) { > ret = -ENOMEM; > - goto out; > + goto out_put_group; > } > > /* > @@ -954,7 +954,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > ret = btrfs_orphan_add(trans, BTRFS_I(inode)); > if (ret) { > btrfs_add_delayed_iput(inode); > - goto out; > + goto out_put_group; > } > clear_nlink(inode); > /* One for the block groups ref */ > @@ -977,13 +977,13 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > > ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1); > if (ret < 0) > - goto out; > + goto out_put_group; > if (ret > 0) > btrfs_release_path(path); > if (ret == 0) { > ret = btrfs_del_item(trans, tree_root, path); > if (ret) > - goto out; > + goto out_put_group; > btrfs_release_path(path); > } > > @@ -1102,7 +1102,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > > ret = remove_block_group_free_space(trans, block_group); > if (ret) > - goto out; > + goto out_put_group; > > btrfs_put_block_group(block_group); > btrfs_put_block_group(block_group); > @@ -1132,6 +1132,9 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > btrfs_delayed_refs_rsv_release(fs_info, 1); > btrfs_free_path(path); > return ret; > +out_put_group: > + btrfs_put_block_group(block_group); > + goto out;
Instead of this double goto, which tends to be error prone and harder to follow, I suggest placing a call to btrfs_put_block_group() right after the 'out' label, with a comment above it saying something like "once for the lookup reference" and removing one of the btrfs_put_block_group() calls right after calling remove_block_group_free_space(), and leaving a comment above the other one saying "once for the block groups rbtree".
Thanks.
> } > > struct btrfs_trans_handle *btrfs_start_trans_remove_block_group( > -- > 2.7.4 >
-- Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
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