[PATCH v3] cgroup/cpuset: Move procfs cpuset attribute under cgroup-v1.c

["Michal Koutný" <mkoutny@suse.com>]

The cpuset file is a legacy attribute that is bound primarily to cpuset
v1 hierarchy (equivalent information is available in /proc/$pid/cgroup path
on the unified hierarchy in conjunction with respective
cgroup.controllers showing where cpuset controller is enabled).

Followup to commit b0ced9d378d49 ("cgroup/cpuset: move v1 interfaces to
cpuset-v1.c") and hide CONFIG_PROC_PID_CPUSET under CONFIG_CPUSETS_V1.
Drop an obsolete comment too.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 init/Kconfig              |  5 +++--
 kernel/cgroup/cpuset-v1.c | 41 +++++++++++++++++++++++++++++++++++
 kernel/cgroup/cpuset.c    | 45 ---------------------------------------
 3 files changed, 44 insertions(+), 47 deletions(-)

v3 changes:
- move dependency on internal cgroup-internal.h to v1-only too
  Reported-by: kernel test robot <lkp@intel.com>
  Link: https://lore.kernel.org/oe-kbuild-all/202501180315.KcDn5BG5-lkp@intel.com/

v2 changes:
- explicitly say what's part of CPUSETS_V1
- commit message wrt effective paths

diff --git a/init/Kconfig b/init/Kconfig
index a20e6efd3f0fb..2f3121c49ed23 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1182,7 +1182,8 @@ config CPUSETS_V1
 	help
 	  Legacy cgroup v1 cpusets controller which has been deprecated by
 	  cgroup v2 implementation. The v1 is there for legacy applications
-	  which haven't migrated to the new cgroup v2 interface yet. If you
+	  which haven't migrated to the new cgroup v2 interface yet. Legacy
+	  interface includes cpuset filesystem and /proc/<pid>/cpuset. If you
 	  do not have any such application then you are completely fine leaving
 	  this option disabled.
 
@@ -1190,7 +1191,7 @@ config CPUSETS_V1
 
 config PROC_PID_CPUSET
 	bool "Include legacy /proc/<pid>/cpuset file"
-	depends on CPUSETS
+	depends on CPUSETS_V1
 	default y
 
 config CGROUP_DEVICE
diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
index 25c1d7b77e2f2..81b5e2a50d587 100644
--- a/kernel/cgroup/cpuset-v1.c
+++ b/kernel/cgroup/cpuset-v1.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include "cgroup-internal.h"
 #include "cpuset-internal.h"
 
 /*
@@ -373,6 +374,46 @@ int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial)
 	return ret;
 }
 
+#ifdef CONFIG_PROC_PID_CPUSET
+/*
+ * proc_cpuset_show()
+ *  - Print tasks cpuset path into seq_file.
+ *  - Used for /proc/<pid>/cpuset.
+ */
+int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
+		     struct pid *pid, struct task_struct *tsk)
+{
+	char *buf;
+	struct cgroup_subsys_state *css;
+	int retval;
+
+	retval = -ENOMEM;
+	buf = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!buf)
+		goto out;
+
+	rcu_read_lock();
+	spin_lock_irq(&css_set_lock);
+	css = task_css(tsk, cpuset_cgrp_id);
+	retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
+				       current->nsproxy->cgroup_ns);
+	spin_unlock_irq(&css_set_lock);
+	rcu_read_unlock();
+
+	if (retval == -E2BIG)
+		retval = -ENAMETOOLONG;
+	if (retval < 0)
+		goto out_free;
+	seq_puts(m, buf);
+	seq_putc(m, '\n');
+	retval = 0;
+out_free:
+	kfree(buf);
+out:
+	return retval;
+}
+#endif /* CONFIG_PROC_PID_CPUSET */
+
 static u64 cpuset_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
 {
 	struct cpuset *cs = css_cs(css);
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 0f910c828973a..5a637292faa20 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -21,7 +21,6 @@
  *  License.  See the file COPYING in the main directory of the Linux
  *  distribution for more details.
  */
-#include "cgroup-internal.h"
 #include "cpuset-internal.h"
 
 #include <linux/init.h>
@@ -4244,50 +4243,6 @@ void cpuset_print_current_mems_allowed(void)
 	rcu_read_unlock();
 }
 
-#ifdef CONFIG_PROC_PID_CPUSET
-/*
- * proc_cpuset_show()
- *  - Print tasks cpuset path into seq_file.
- *  - Used for /proc/<pid>/cpuset.
- *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
- *    doesn't really matter if tsk->cpuset changes after we read it,
- *    and we take cpuset_mutex, keeping cpuset_attach() from changing it
- *    anyway.
- */
-int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
-		     struct pid *pid, struct task_struct *tsk)
-{
-	char *buf;
-	struct cgroup_subsys_state *css;
-	int retval;
-
-	retval = -ENOMEM;
-	buf = kmalloc(PATH_MAX, GFP_KERNEL);
-	if (!buf)
-		goto out;
-
-	rcu_read_lock();
-	spin_lock_irq(&css_set_lock);
-	css = task_css(tsk, cpuset_cgrp_id);
-	retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
-				       current->nsproxy->cgroup_ns);
-	spin_unlock_irq(&css_set_lock);
-	rcu_read_unlock();
-
-	if (retval == -E2BIG)
-		retval = -ENAMETOOLONG;
-	if (retval < 0)
-		goto out_free;
-	seq_puts(m, buf);
-	seq_putc(m, '\n');
-	retval = 0;
-out_free:
-	kfree(buf);
-out:
-	return retval;
-}
-#endif /* CONFIG_PROC_PID_CPUSET */
-
 /* Display task mems_allowed in /proc/<pid>/status file. */
 void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
 {
-- 
2.47.1