[SRU][J][PATCH 2/5] cgroup: Homogenize cgroup_get_from_id() return value

[Philip Cox]

From: Michal Koutný <mkoutny at suse.com>

Cgroup id is user provided datum hence extend its return domain to
include possible error reason (similar to cgroup_get_from_fd()).

This change also fixes commit d4ccaf58a847 ("bpf: Introduce cgroup
iter") that would use NULL instead of proper error handling in
d4ccaf58a847 ("bpf: Introduce cgroup iter").

Additionally, neither of: fc_appid_store, bpf_iter_attach_cgroup,
mem_cgroup_get_from_ino (callers of cgroup_get_from_fd) is built without
CONFIG_CGROUPS (depends via CONFIG_BLK_CGROUP, direct, transitive
CONFIG_MEMCG respectively) transitive, so drop the singular definition
not needed with !CONFIG_CGROUPS.

Fixes: d4ccaf58a847 ("bpf: Introduce cgroup iter")
Signed-off-by: Michal Koutný <mkoutny at suse.com>
Signed-off-by: Tejun Heo <tj at kernel.org>
(backported from commit fa7e439cf90ba23ea473d0b7d85efd02ae6ccf94)
[philcox: context changes around mem_cgroup_get_from_ino()]
Signed-off-by: Philip Cox <philip.cox at canonical.com>
---
 include/linux/cgroup.h |  5 -----
 kernel/cgroup/cgroup.c |  4 ++--
 mm/memcontrol.c        | 23 +++++++++++++++++++++++
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 0d97d1cf660f7..92a147bfacbbd 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -753,11 +753,6 @@ static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 
 static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 {}
-
-static inline struct cgroup *cgroup_get_from_id(u64 id)
-{
-	return NULL;
-}
 #endif /* !CONFIG_CGROUPS */
 
 #ifdef CONFIG_CGROUPS
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 27d503fd17fe5..219a138e22923 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6032,7 +6032,7 @@ void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 /*
  * cgroup_get_from_id : get the cgroup associated with cgroup id
  * @id: cgroup id
- * On success return the cgrp, on failure return NULL
+ * On success return the cgrp or ERR_PTR on failure
  * Only cgroups within current task's cgroup NS are valid.
  */
 struct cgroup *cgroup_get_from_id(u64 id)
@@ -6068,7 +6068,7 @@ struct cgroup *cgroup_get_from_id(u64 id)
 		cgrp = NULL;
 	}
 out:
-	return cgrp;
+	return cgrp ?: ERR_PTR(-ENOENT);
 }
 EXPORT_SYMBOL_GPL(cgroup_get_from_id);
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63a03ec849353..16619f3b2f119 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5149,6 +5149,29 @@ struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 	return idr_find(&mem_cgroup_idr, id);
 }
 
+#ifdef CONFIG_SHRINKER_DEBUG
+struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
+{
+	struct cgroup *cgrp;
+	struct cgroup_subsys_state *css;
+	struct mem_cgroup *memcg;
+
+	cgrp = cgroup_get_from_id(ino);
+	if (IS_ERR(cgrp))
+		return PTR_ERR(cgrp);
+
+	css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
+	if (css)
+		memcg = container_of(css, struct mem_cgroup, css);
+	else
+		memcg = ERR_PTR(-ENOENT);
+
+	cgroup_put(cgrp);
+
+	return memcg;
+}
+#endif
+
 static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 {
 	struct mem_cgroup_per_node *pn;
-- 
2.43.0