[PATCH v6 01/12] cgroup/misc: Add per resource callbacks for CSS events

[Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>]

From: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>

The misc cgroup controller (subsystem) currently does not perform
resource type specific action for Cgroups Subsystem State (CSS) events:
the 'css_alloc' event when a cgroup is created and the 'css_free' event
when a cgroup is destroyed.

Define callbacks for those events and allow resource providers to
register the callbacks per resource type as needed. This will be
utilized later by the EPC misc cgroup support implemented in the SGX
driver.

Also add per resource type private data for those callbacks to store and
access resource specific data.

Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
Co-developed-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
---
V6:
- Create ops struct for per resource callbacks (Jarkko)
- Drop max_write callback (Dave, Michal)
- Style fixes (Kai)
---
 include/linux/misc_cgroup.h | 14 ++++++++++++++
 kernel/cgroup/misc.c        | 27 ++++++++++++++++++++++++---
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
index e799b1f8d05b..5dc509c27c3d 100644
--- a/include/linux/misc_cgroup.h
+++ b/include/linux/misc_cgroup.h
@@ -27,16 +27,30 @@ struct misc_cg;
 
 #include <linux/cgroup.h>
 
+/**
+ * struct misc_operations_struct: per resource callback ops.
+ * @alloc: invoked for resource specific initialization when cgroup is allocated.
+ * @free: invoked for resource specific cleanup when cgroup is deallocated.
+ */
+struct misc_operations_struct {
+	int (*alloc)(struct misc_cg *cg);
+	void (*free)(struct misc_cg *cg);
+};
+
 /**
  * struct misc_res: Per cgroup per misc type resource
  * @max: Maximum limit on the resource.
  * @usage: Current usage of the resource.
  * @events: Number of times, the resource limit exceeded.
+ * @priv: resource specific data.
+ * @misc_ops: resource specific operations.
  */
 struct misc_res {
 	u64 max;
 	atomic64_t usage;
 	atomic64_t events;
+	void *priv;
+	const struct misc_operations_struct *misc_ops;
 };
 
 /**
diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
index 79a3717a5803..d971ede44ebf 100644
--- a/kernel/cgroup/misc.c
+++ b/kernel/cgroup/misc.c
@@ -383,23 +383,37 @@ static struct cftype misc_cg_files[] = {
 static struct cgroup_subsys_state *
 misc_cg_alloc(struct cgroup_subsys_state *parent_css)
 {
+	struct misc_cg *parent_cg, *cg;
 	enum misc_res_type i;
-	struct misc_cg *cg;
+	int ret;
 
 	if (!parent_css) {
-		cg = &root_cg;
+		parent_cg = cg = &root_cg;
 	} else {
 		cg = kzalloc(sizeof(*cg), GFP_KERNEL);
 		if (!cg)
 			return ERR_PTR(-ENOMEM);
+		parent_cg = css_misc(parent_css);
 	}
 
 	for (i = 0; i < MISC_CG_RES_TYPES; i++) {
 		WRITE_ONCE(cg->res[i].max, MAX_NUM);
 		atomic64_set(&cg->res[i].usage, 0);
+		if (parent_cg->res[i].misc_ops && parent_cg->res[i].misc_ops->alloc) {
+			ret = parent_cg->res[i].misc_ops->alloc(cg);
+			if (ret)
+				goto alloc_err;
+		}
 	}
 
 	return &cg->css;
+
+alloc_err:
+	for (i = 0; i < MISC_CG_RES_TYPES; i++)
+		if (parent_cg->res[i].misc_ops && parent_cg->res[i].misc_ops->free)
+			cg->res[i].misc_ops->free(cg);
+	kfree(cg);
+	return ERR_PTR(ret);
 }
 
 /**
@@ -410,7 +424,14 @@ misc_cg_alloc(struct cgroup_subsys_state *parent_css)
  */
 static void misc_cg_free(struct cgroup_subsys_state *css)
 {
-	kfree(css_misc(css));
+	struct misc_cg *cg = css_misc(css);
+	enum misc_res_type i;
+
+	for (i = 0; i < MISC_CG_RES_TYPES; i++)
+		if (cg->res[i].misc_ops && cg->res[i].misc_ops->free)
+			cg->res[i].misc_ops->free(cg);
+
+	kfree(cg);
 }
 
 /* Cgroup controller callbacks */
-- 
2.25.1