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SubjectRe: [PATCH 2/2] drivers: core: Remove glue dirs from sysfs earlier
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On Tue, 2018-07-03 at 12:39 +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2018-07-02 at 19:26 -0700, Linus Torvalds wrote:
> > On Mon, Jul 2, 2018 at 7:15 PM Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > It's whitespace-damaged on purpose. It's probably broken shit. DO NOT
> > > USE UNDER ANY CIRCUMSTANCES. Think of it more as a "something like
> > > this might work, but probably doesn't". Maybe it gives you an idea,
> > > although that idea might be "Linus has finally lost it".
> >
> > Even if it were to work, it should probably just be done inside kernfs
> > and exposed as some kind of "kernfs_remove_if_empty()" function.
>
> That would be harder, we'd have to expose it via a
> kobject_del_if_empty() then.
>
> Since we control completely when things are added/removed from the
> gluedir and have a big fat mutex for it, I don't think locking is much
> of an issue. At least in that specific case.

Ok, kernfs was a tad tougher to crack than I hoped but here's a
prototype lightly tested.

Tejun, Greg, does it look reasonable to you ?

Cheers,
Ben.

diff --git a/drivers/base/core.c b/drivers/base/core.c
index b610816eb887..9166f68276c6 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1570,6 +1570,8 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
return;

mutex_lock(&gdp_mutex);
+ if (!kobject_has_children(glue_dir))
+ kobject_del(glue_dir);
kobject_put(glue_dir);
mutex_unlock(&gdp_mutex);
}
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 89d1dc19340b..e4bec09bc602 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1251,6 +1251,29 @@ void kernfs_activate(struct kernfs_node *kn)
mutex_unlock(&kernfs_mutex);
}

+bool kernfs_has_children(struct kernfs_node *kn)
+{
+ bool has_children = false;
+ struct kernfs_node *pos;
+
+ /* Lockless shortcut */
+ if (RB_EMPTY_NODE(&kn->rb))
+ return false;
+
+ /* Now check for active children */
+ mutex_lock(&kernfs_mutex);
+ pos = NULL;
+ while ((pos = kernfs_next_descendant_post(pos, kn)) && pos != kn) {
+ if (kernfs_active(pos)) {
+ has_children = true;
+ break;
+ }
+ }
+ mutex_unlock(&kernfs_mutex);
+
+ return has_children;
+}
+
static void __kernfs_remove(struct kernfs_node *kn)
{
struct kernfs_node *pos;
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index ab25c8b6d9e3..776350ac1cbc 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -300,6 +300,12 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
return kn->flags & KERNFS_NS;
}

+/**
+ * kernfs_has_children - Returns whether a kernfs node has children.
+ * @kn: the node to test
+ */
+bool kernfs_has_children(struct kernfs_node *kn);
+
int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
char *buf, size_t buflen);
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 7f6f93c3df9c..1e3294ab95f0 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -116,6 +116,17 @@ extern void kobject_put(struct kobject *kobj);
extern const void *kobject_namespace(struct kobject *kobj);
extern char *kobject_get_path(struct kobject *kobj, gfp_t flag);

+/**
+ * kobject_has_children - Returns whether a kobject has children.
+ * @kobj: the object to test
+ */
+static inline bool kobject_has_children(struct kobject *kobj)
+{
+ WARN_ON_ONCE(kref_read(&kobj->kref) == 0);
+
+ return kobj->sd && kernfs_has_children(kobj->sd);
+}
+
struct kobj_type {
void (*release)(struct kobject *kobj);
const struct sysfs_ops *sysfs_ops;
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