From: Muneendra Kumar <muneendra.kumar@broadcom.com>
Date: Tue, 8 Jun 2021 10:05:44 +0530
Subject: scsi: cgroup: Add cgroup_get_from_id()
Patch-mainline: v5.14-rc1
Git-commit: 6b658c4863c15936872a93c9ee879043bf6393c9
References: bsc#1189385 jsc#SLE-18970

Add a new function, cgroup_get_from_id(), to retrieve the cgroup associated
with a cgroup id. Also export the function cgroup_get_e_css() as this is
needed in blk-cgroup.h.

Link: https://lore.kernel.org/r/20210608043556.274139-2-muneendra.kumar@broadcom.com
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Muneendra Kumar <muneendra.kumar@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[dwagner: replace kernfs_find_and_get_node_by_id by kernfs_get_node_by_id]
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 include/linux/cgroup.h |    6 ++++++
 kernel/cgroup/cgroup.c |   27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -696,6 +696,7 @@ static inline union kernfs_node_id *cgro
 
 void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
 					char *buf, size_t buflen);
+struct cgroup *cgroup_get_from_id(u64 id);
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;
@@ -743,6 +744,11 @@ static inline bool task_under_cgroup_hie
 
 static inline void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
 	char *buf, size_t buflen) {}
+
+static inline struct cgroup *cgroup_get_from_id(u64 id)
+{
+	return NULL;
+}
 #endif /* !CONFIG_CGROUPS */
 
 #ifdef CONFIG_CGROUPS
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -587,6 +587,7 @@ struct cgroup_subsys_state *cgroup_get_e
 	rcu_read_unlock();
 	return css;
 }
+EXPORT_SYMBOL_GPL(cgroup_get_e_css);
 
 static void cgroup_get_live(struct cgroup *cgrp)
 {
@@ -5886,6 +5887,32 @@ void cgroup_path_from_kernfs_id(const un
 }
 
 /*
+ * cgroup_get_from_id : get the cgroup associated with cgroup id
+ * @id: cgroup id
+ * On success return the cgrp, on failure return NULL
+ */
+struct cgroup *cgroup_get_from_id(u64 id)
+{
+	struct kernfs_node *kn;
+	struct cgroup *cgrp = NULL;
+	const union kernfs_node_id nid = { .id = id };
+
+	mutex_lock(&cgroup_mutex);
+	kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, &nid);
+	if (!kn)
+		goto out_unlock;
+
+	cgrp = kn->priv;
+	if (cgroup_is_dead(cgrp) || !cgroup_tryget(cgrp))
+		cgrp = NULL;
+	kernfs_put(kn);
+out_unlock:
+	mutex_unlock(&cgroup_mutex);
+	return cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_get_from_id);
+
+/*
  * proc_cgroup_show()
  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
  *  - Used for /proc/<pid>/cgroup.