Re: [PATCH 09/18] fs: rework icount to be a locked variable

Christoph Hellwig
2010-10-08T07:27:53Z

> index 2953e9f..9f04478 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1964,8 +1964,14 @@ void btrfs_add_delayed_iput(struct inode *inode)
> struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
> struct delayed_iput *delayed;
>
> - if (atomic_add_unless(&inode->i_count, -1, 1))
> + /* XXX: filesystems should not play refcount games like this */
> + spin_lock(&inode->i_lock);
> + if (inode->i_ref > 1) {
> + inode->i_ref--;
> + spin_unlock(&inode->i_lock);
> return;
> + }
> + spin_unlock(&inode->i_lock);

Yeah, all that i_count/i_ref mess in btrfs needs some serious work.
Chris?

> +
> +/*
> + * inode_lock must be held
> + */
> +void iref_locked(struct inode *inode)
> +{
> + inode->i_ref++;
> +}
> EXPORT_SYMBOL_GPL(iref_locked);

I'm a big fan of _GPL exports, but adding this for a trivial counter
increment seems a bit weird.

> int iref_read(struct inode *inode)
> {
> - return atomic_read(&inode->i_count);
> + int ref;
> +
> + spin_lock(&inode->i_lock);
> + ref = inode->i_ref;
> + spin_unlock(&inode->i_lock);
> + return ref;
> }

There's no need to lock a normal 32-bit variable for readers.

> + inode->i_ref--;
> + if (inode->i_ref == 0) {

if (--inode->i_ref == 0) {

might be a bit more idiomatic.