[Devel] Re: [PATCH 14/25] sysfs: Don't use lookup_one_len_kern

[Tejun Heo]

On Tue, Aug 07, 2007 at 03:23:57PM -0600, Eric W. Biederman wrote:
> 
> Upon inspection it appears that there is no looking of the
> inode mutex in lookup_one_len_kern and we aren't calling
> it with the inode mutex and that is wrong.
> 
> So this patch rolls our own dcache insertion function that
> does exactly what we need it to do.  As it turns out this
> is pretty trivial to do and it makes the code easier to
> audit.
> 
> Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
> ---
>  fs/sysfs/dir.c |   41 +++++++++++++++++++++++++++++++++++++++--
>  1 files changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index a9bdb12..1d53c2a 100644
> --- a/fs/sysfs/dir.c
> +++ b/fs/sysfs/dir.c
> @@ -765,6 +765,44 @@ static struct dentry *__sysfs_get_dentry(struct super_block *sb, struct sysfs_di
>  	return dentry;
>  }
>  
> +static struct dentry *sysfs_add_dentry(struct dentry *parent, struct sysfs_dirent *sd)
> +{
> +	struct qstr name;
> +	struct dentry *dentry;
> +	struct inode *inode;
> +
> +	mutex_lock(&parent->d_inode->i_mutex);
> +	mutex_lock(&sysfs_mutex);
> +	dentry = ERR_PTR(-EINVAL);
> +	if (parent->d_fsdata != sd->s_parent)
> +		goto out;
> +
> +	name.name = sd->s_name;
> +	name.len = strlen(sd->s_name);
> +	dentry = d_hash_and_lookup(parent, &name);
> +	if (dentry)
> +		goto out;
> +
> +	dentry = d_alloc(parent, &name);
> +	if (!dentry) {
> +		dentry = ERR_PTR(-ENOMEM);
> +		goto out;
> +	}
> +
> +	inode = sysfs_get_inode(sd);
> +	if (!inode) {
> +		dput(dentry);
> +		dentry = ERR_PTR(-ENOMEM);
> +		goto out;
> +	}
> +	d_instantiate(dentry, inode);
> +	sysfs_attach_dentry(sd, dentry);
> +out:
> +	mutex_unlock(&sysfs_mutex);
> +	mutex_unlock(&parent->d_inode->i_mutex);
> +	return dentry;
> +}

This is virtually identical to

	mutex_lock(&parent_dentry->d_inode->i_mutex);
	dentry = lookup_one_len_kern(cur->s_name, parent_dentry,
				     strlen(cur->s_name));
	mutex_unlock(&parent_dentry->d_inode->i_mutex);

right?  I don't think we need to duplicate the code here.  Or is it
needed for later multi-sb thing?

-- 
tejun
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