On Wed, Sep 04, 2013 at 04:05:48PM +0200, Miklos Szeredi wrote:
> +static void check_and_drop(void *_data, struct dentry *dentry)
> +{
> + struct select_data *data = _data;
> +
> + /* We're only interested in the root of this subtree */
> + if (data->start == dentry) {
> + if (d_mountpoint(dentry))
> + data->found = -EBUSY;
> + if (!data->found)
> + __d_drop(dentry);
> + }
> +}
Wouldn't it be better to do that in caller? Granted, it's not a hot
path, but... why bother calling it for each dentry in a subtree, only
to return immediately on all calls but the last one?
> +static int __check_submounts_and_drop(struct dentry *parent,
> + struct list_head *dispose)
> +{
> + struct select_data data = {
> + .start = parent,
> + .dispose = dispose,
> + .found = 0,
> + };
> +
> + d_walk(parent, &data, check_and_collect, check_and_drop);
> +
> + return data.found;
> +}
Incidentally, I would rather expand that in the only caller...
> +/**
> + * check_submounts_and_drop - prune dcache, check for submounts and drop
> + *
> + * All done as a single atomic operation relative to has_unlinked_ancestor().
> + * Returns 0 if successfully unhashed @parent. If there were submounts then
> + * return -EBUSY.
> + *
> + * @dentry: dentry to prune and drop
> + */
> +int check_submounts_and_drop(struct dentry *dentry)
> +{
> + int ret = 0;
> +
> + /* Negative dentries can be dropped without further checks */
> + if (!dentry->d_inode) {
> + d_drop(dentry);
> + goto out;
> + }
> +
> + spin_lock(&dentry->d_lock);
> + if (d_unhashed(dentry))
> + goto out_unlock;
> + if (list_empty(&dentry->d_subdirs)) {
> + if (d_mountpoint(dentry)) {
> + ret = -EBUSY;
> + goto out_unlock;
> + }
> + __d_drop(dentry);
> + goto out_unlock;
> + }
> + spin_unlock(&dentry->d_lock);
> +
> + for (;;) {
> + LIST_HEAD(dispose);
> + ret = __check_submounts_and_drop(dentry, &dispose);
> + if (!list_empty(&dispose))
> + shrink_dentry_list(&dispose);
> +
> + if (ret <= 0)
> + break;
> +
> + cond_resched();
> + }
> +
> +out:
> + return ret;
> +
> +out_unlock:
> + spin_unlock(&dentry->d_lock);
> + goto out;
> +}
> +EXPORT_SYMBOL(check_submounts_and_drop);
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