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

[Philip Cox]

From: Michal Koutný <mkoutny at suse.com>

BugLink: https://bugs.launchpad.net/bugs/2089318

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 in blkcg_set_fc_appid() and
around mem_cgroup_get_from_ino()]

Signed-off-by: Philip Cox <philip.cox at canonical.com>
---
 include/linux/blk-cgroup.h | 4 ++--
 include/linux/cgroup.h     | 5 -----
 kernel/cgroup/cgroup.c     | 4 ++--
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 27c363f6b281b..cb9cb23034a9f 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -705,8 +705,8 @@ static inline int blkcg_set_fc_appid(char *app_id, u64 cgrp_id, size_t app_id_le
 		return -EINVAL;
 
 	cgrp = cgroup_get_from_id(cgrp_id);
-	if (!cgrp)
-		return -ENOENT;
+	if (IS_ERR(cgrp))
+		return PTR_ERR(cgrp);
 	css = cgroup_get_e_css(cgrp, &io_cgrp_subsys);
 	if (!css) {
 		ret = -ENOENT;
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);
 
-- 
2.43.0