[PATCH 2/3] cgroup: Return ERR_PTR from cgroup_kn_lock_live()
From: Tejun Heo
Date: Wed Sep 02 2026 - 19:15:31 EST
cgroup_kn_lock_live() returns NULL when the cgroup is dead and the callers
translate that into an errno themselves. Return ERR_PTR(-ENODEV) instead and
have the callers pass the errno through, so that failures other than a dead
cgroup can be reported through the same return value. No functional change.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/cgroup/cgroup-v1.c | 8 +++----
kernel/cgroup/cgroup.c | 50 +++++++++++++++++++--------------------
kernel/cgroup/debug.c | 10 ++++----
3 files changed, 34 insertions(+), 34 deletions(-)
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index a4337c9b5287..7e008867f3ac 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -506,8 +506,8 @@ static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
enum cgroup_attach_lock_mode lock_mode;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
task = cgroup_procs_write_start(buf, threadgroup, &lock_mode);
ret = PTR_ERR_OR_ZERO(task);
@@ -569,8 +569,8 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
return -EPERM;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
spin_lock(&release_agent_path_lock);
strscpy(cgrp->root->release_agent_path, strstrip(buf),
sizeof(cgrp->root->release_agent_path));
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 37bc8a67a40f..61a201bed71a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1685,8 +1685,8 @@ void cgroup_kn_unlock(struct kernfs_node *kn)
* This helper is to be used by a cgroup kernfs method currently servicing
* @kn. It breaks the active protection, performs cgroup locking and
* verifies that the associated cgroup is alive. Returns the cgroup if
- * alive; otherwise, %NULL. A successful return should be undone by a
- * matching cgroup_kn_unlock() invocation. If @drain_offline is %true, the
+ * alive; otherwise, an ERR_PTR value. A successful return should be undone by
+ * a matching cgroup_kn_unlock() invocation. If @drain_offline is %true, the
* cgroup is drained of offlining csses before return.
*
* Any cgroup kernfs method implementation which requires locking the
@@ -1710,7 +1710,7 @@ struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
* break the active_ref protection.
*/
if (!cgroup_tryget(cgrp))
- return NULL;
+ return ERR_PTR(-ENODEV);
kernfs_break_active_protection(kn);
if (drain_offline)
@@ -1722,7 +1722,7 @@ struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
return cgrp;
cgroup_kn_unlock(kn);
- return NULL;
+ return ERR_PTR(-ENODEV);
}
static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
@@ -3650,8 +3650,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
}
cgrp = cgroup_kn_lock_live(of->kn, true);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
for_each_subsys(ss, ssid) {
if (enable & (1 << ssid)) {
@@ -3790,8 +3790,8 @@ static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
/* drain dying csses before we re-apply (threaded) subtree control */
cgrp = cgroup_kn_lock_live(of->kn, true);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
/* threaded can only be enabled */
ret = cgroup_enable_threaded(cgrp);
@@ -3833,8 +3833,8 @@ static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
return -ERANGE;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
WRITE_ONCE(cgrp->max_descendants, descendants);
@@ -3876,8 +3876,8 @@ static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
return -ERANGE;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
WRITE_ONCE(cgrp->max_depth, depth);
@@ -4075,8 +4075,8 @@ static ssize_t pressure_write(struct kernfs_open_file *of, char *buf,
ssize_t ret = 0;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
ctx = of->priv;
if (!ctx) {
@@ -4192,8 +4192,8 @@ static ssize_t cgroup_pressure_write(struct kernfs_open_file *of,
return -ERANGE;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
psi = cgroup_psi(cgrp);
if (psi->enabled != enable) {
@@ -4268,8 +4268,8 @@ static ssize_t cgroup_freeze_write(struct kernfs_open_file *of,
return -ERANGE;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
cgroup_freeze(cgrp, freeze);
@@ -4330,8 +4330,8 @@ static ssize_t cgroup_kill_write(struct kernfs_open_file *of, char *buf,
return -ERANGE;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
/*
* Killing is a process directed operation, i.e. the whole thread-group
@@ -5485,8 +5485,8 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
enum cgroup_attach_lock_mode lock_mode;
dst_cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!dst_cgrp)
- return -ENODEV;
+ if (IS_ERR(dst_cgrp))
+ return PTR_ERR(dst_cgrp);
task = cgroup_procs_write_start(buf, threadgroup, &lock_mode);
ret = PTR_ERR_OR_ZERO(task);
@@ -6120,8 +6120,8 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
return -EINVAL;
parent = cgroup_kn_lock_live(parent_kn, false);
- if (!parent)
- return -ENODEV;
+ if (IS_ERR(parent))
+ return PTR_ERR(parent);
if (!cgroup_check_hierarchy_limits(parent)) {
ret = -EAGAIN;
@@ -6397,7 +6397,7 @@ int cgroup_rmdir(struct kernfs_node *kn)
int ret = 0;
cgrp = cgroup_kn_lock_live(kn, false);
- if (!cgrp)
+ if (IS_ERR(cgrp))
return 0;
ret = cgroup_destroy_locked(cgrp);
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 883347b87842..96004cd65d09 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -45,7 +45,7 @@ static int current_css_set_read(struct seq_file *seq, void *v)
struct cgroup_subsys_state *css;
int i, refcnt;
- if (!cgroup_kn_lock_live(of->kn, false))
+ if (IS_ERR(cgroup_kn_lock_live(of->kn, false)))
return -ENODEV;
spin_lock_irq(&css_set_lock);
@@ -206,8 +206,8 @@ static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
int i;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
for_each_subsys(ss, i) {
css = rcu_dereference_check(cgrp->subsys[ss->id], true);
@@ -254,8 +254,8 @@ static int cgroup_masks_read(struct seq_file *seq, void *v)
struct cgroup *cgrp;
cgrp = cgroup_kn_lock_live(of->kn, false);
- if (!cgrp)
- return -ENODEV;
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
cgroup_masks_read_one(seq, "subtree_control", cgrp->subtree_control);
cgroup_masks_read_one(seq, "subtree_ss_mask", cgrp->subtree_ss_mask);
--
2.55.0