cgroup: Homogenize cgroup_get_from_id() return value

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2077665

commit fa7e439
Author: Michal Koutný <mkoutny@suse.com>
Date:   Fri, 26 Aug 2022 18:52:37 +0200

    cgroup: Homogenize cgroup_get_from_id() return value

    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 d4ccaf5 ("bpf: Introduce cgroup
    iter") that would use NULL instead of proper error handling in
    d4ccaf5 ("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: d4ccaf5 ("bpf: Introduce cgroup iter")
    Signed-off-by: Michal Koutný <mkoutny@suse.com>
    Signed-off-by: Tejun Heo <tj@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

block/blk-cgroup-fc-appid.c

@@ -19,8 +19,8 @@ int blkcg_set_fc_appid(char *app_id, u64 cgrp_id, size_t app_id_len)
 		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;

include/linux/cgroup.h

@@ -752,11 +752,6 @@ 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

kernel/cgroup/cgroup.c

@@ -6020,7 +6020,7 @@ 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)
@@ -6056,7 +6056,7 @@ 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);
 

mm/memcontrol.c

@@ -5146,8 +5146,8 @@ struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
 	struct mem_cgroup *memcg;
 
 	cgrp = cgroup_get_from_id(ino);
-	if (!cgrp)
-		return ERR_PTR(-ENOENT);
+	if (IS_ERR(cgrp))
+		return PTR_ERR(cgrp);
 
 	css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
 	if (css)