cgroup: Implement DEBUG_CGROUP_REF

It's really difficult to debug when cgroup or css refs leak. Let's add a
debug option to force the refcnt function to not be inlined so that they can
be kprobed for debugging.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 90 insertions, 0 deletions

diff --git a/include/linux/cgroup_refcnt.h b/include/linux/cgroup_refcnt.h
new file mode 100644
index 000000000000..1aa89295dac0
--- /dev/null
+++ b/include/linux/cgroup_refcnt.h
@@ -0,0 +1,90 @@
+/**
+ * css_get - obtain a reference on the specified css
+ * @css: target css
+ *
+ * The caller must already have a reference.
+ */
+CGROUP_REF_FN_ATTRS
+void css_get(struct cgroup_subsys_state *css)
+{
+	if (!(css->flags & CSS_NO_REF))
+		percpu_ref_get(&css->refcnt);
+}
+
+/**
+ * css_get_many - obtain references on the specified css
+ * @css: target css
+ * @n: number of references to get
+ *
+ * The caller must already have a reference.
+ */
+CGROUP_REF_FN_ATTRS
+void css_get_many(struct cgroup_subsys_state *css, unsigned int n)
+{
+	if (!(css->flags & CSS_NO_REF))
+		percpu_ref_get_many(&css->refcnt, n);
+}
+
+/**
+ * css_tryget - try to obtain a reference on the specified css
+ * @css: target css
+ *
+ * Obtain a reference on @css unless it already has reached zero and is
+ * being released.  This function doesn't care whether @css is on or
+ * offline.  The caller naturally needs to ensure that @css is accessible
+ * but doesn't have to be holding a reference on it - IOW, RCU protected
+ * access is good enough for this function.  Returns %true if a reference
+ * count was successfully obtained; %false otherwise.
+ */
+CGROUP_REF_FN_ATTRS
+bool css_tryget(struct cgroup_subsys_state *css)
+{
+	if (!(css->flags & CSS_NO_REF))
+		return percpu_ref_tryget(&css->refcnt);
+	return true;
+}
+
+/**
+ * css_tryget_online - try to obtain a reference on the specified css if online
+ * @css: target css
+ *
+ * Obtain a reference on @css if it's online.  The caller naturally needs
+ * to ensure that @css is accessible but doesn't have to be holding a
+ * reference on it - IOW, RCU protected access is good enough for this
+ * function.  Returns %true if a reference count was successfully obtained;
+ * %false otherwise.
+ */
+CGROUP_REF_FN_ATTRS
+bool css_tryget_online(struct cgroup_subsys_state *css)
+{
+	if (!(css->flags & CSS_NO_REF))
+		return percpu_ref_tryget_live(&css->refcnt);
+	return true;
+}
+
+/**
+ * css_put - put a css reference
+ * @css: target css
+ *
+ * Put a reference obtained via css_get() and css_tryget_online().
+ */
+CGROUP_REF_FN_ATTRS
+void css_put(struct cgroup_subsys_state *css)
+{
+	if (!(css->flags & CSS_NO_REF))
+		percpu_ref_put(&css->refcnt);
+}
+
+/**
+ * css_put_many - put css references
+ * @css: target css
+ * @n: number of references to put
+ *
+ * Put references obtained via css_get() and css_tryget_online().
+ */
+CGROUP_REF_FN_ATTRS
+void css_put_many(struct cgroup_subsys_state *css, unsigned int n)
+{
+	if (!(css->flags & CSS_NO_REF))
+		percpu_ref_put_many(&css->refcnt, n);
+}