[PATCH 2/2][v2] x86/resctrl: Add task resctrl information display

[Chen Yu <yu.c.chen@intel.com>]

Monitoring tools that want to find out which resctrl CTRL
and MONITOR groups a task belongs to must currently read
the "tasks" file in every group until they locate the process
ID.

Add an additional file /proc/{pid}/resctrl to provide this
information.

For example:
 cat /proc/1193/resctrl
CTRL_MON:/ctrl_grp0
MON:/ctrl_grp0/mon_groups/mon_grp0

If the resctrl filesystem has not been mounted,
reading /proc/{pid}/resctrl returns an error:
cat: /proc/1193/resctrl: No such device

Tested-by: Jinshi Chen <jinshi.chen@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>

---
v2: Reduce indentation level in proc_resctrl_show()
    according to Boris's suggestion.
    Create the include/linux/resctrl.h header and
    declare proc_resctrl_show() in this file, so
    that other architectures would probably use it
    in the future. Different architectures should
    implement architectural specific proc_resctrl_show()
    accordingly.
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 47 ++++++++++++++++++++++++++
 fs/proc/base.c                         |  7 ++++
 include/linux/resctrl.h                | 16 +++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 include/linux/resctrl.h

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index a46dee8e78db..b53bf52a04f5 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -727,6 +727,53 @@ static int rdtgroup_tasks_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
+		      struct pid *pid, struct task_struct *tsk)
+{
+	struct rdtgroup *rdtg;
+	int ret = 0;
+
+	mutex_lock(&rdtgroup_mutex);
+
+	/* Make sure resctrl has been mounted. */
+	if (!static_branch_unlikely(&rdt_enable_key)) {
+		ret = -ENODEV;
+		goto unlock;
+	}
+
+	list_for_each_entry(rdtg, &rdt_all_groups, rdtgroup_list) {
+		struct rdtgroup *crg;
+
+		/*
+		 * Task information is only relevant for shareable
+		 * and exclusive groups.
+		 */
+		if (rdtg->mode != RDT_MODE_SHAREABLE &&
+		    rdtg->mode != RDT_MODE_EXCLUSIVE)
+			continue;
+
+		if (rdtg->closid != tsk->closid)
+			continue;
+
+		seq_printf(s, "CTRL_MON:/%s\n", rdtg->kn->name);
+		list_for_each_entry(crg, &rdtg->mon.crdtgrp_list,
+				    mon.crdtgrp_list) {
+			if (tsk->rmid != crg->mon.rmid)
+				continue;
+			seq_printf(s, "MON:%s%s/mon_groups/%s\n",
+				   rdtg == &rdtgroup_default ? "" : "/",
+				   rdtg->kn->name, crg->kn->name);
+			goto unlock;
+		}
+		goto unlock;
+	}
+	ret = -ENOENT;
+unlock:
+	mutex_unlock(&rdtgroup_mutex);
+
+	return ret;
+}
+
 static int rdt_last_cmd_status_show(struct kernfs_open_file *of,
 				    struct seq_file *seq, void *v)
 {
diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb8..3ddcb0cae3bd 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -94,6 +94,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/stat.h>
 #include <linux/posix-timers.h>
+#include <linux/resctrl.h>
 #include <trace/events/oom.h>
 #include "internal.h"
 #include "fd.h"
@@ -3060,6 +3061,9 @@ static const struct pid_entry tgid_base_stuff[] = {
 #endif
 #ifdef CONFIG_CGROUPS
 	ONE("cgroup",  S_IRUGO, proc_cgroup_show),
+#endif
+#ifdef CONFIG_CPU_RESCTRL
+	ONE("resctrl", S_IRUGO, proc_resctrl_show),
 #endif
 	ONE("oom_score",  S_IRUGO, proc_oom_score),
 	REG("oom_adj",    S_IRUGO|S_IWUSR, proc_oom_adj_operations),
@@ -3460,6 +3464,9 @@ static const struct pid_entry tid_base_stuff[] = {
 #endif
 #ifdef CONFIG_CGROUPS
 	ONE("cgroup",  S_IRUGO, proc_cgroup_show),
+#endif
+#ifdef CONFIG_CPU_RESCTRL
+	ONE("resctrl", S_IRUGO, proc_resctrl_show),
 #endif
 	ONE("oom_score", S_IRUGO, proc_oom_score),
 	REG("oom_adj",   S_IRUGO|S_IWUSR, proc_oom_adj_operations),
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
new file mode 100644
index 000000000000..9f0e6a892cb3
--- /dev/null
+++ b/include/linux/resctrl.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _CPU_RESCTRL_H
+#define _CPU_RESCTRL_H
+
+#ifdef CONFIG_CPU_RESCTRL
+
+#include <linux/proc_fs.h>
+
+int proc_resctrl_show(struct seq_file *m,
+		      struct pid_namespace *ns,
+		      struct pid *pid,
+		      struct task_struct *tsk);
+
+#endif
+
+#endif /* _CPU_RESCTRL_H */
-- 
2.17.1