[patch v9 04/10] procfs: add per-pid task isolation state

[Marcelo Tosatti <mtosatti@redhat.com>]

The logic to disable vmstat worker thread, when entering
nohz full, does not cover all scenarios. For example, it is possible
for the following to happen:
References: <20220127172319.428529308@fuller.cnet>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8

Add /proc/pid/task_isolation file, to query the state of
task isolation configuration.

---
 fs/proc/base.c |   68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

Index: linux-2.6/fs/proc/base.c
===================================================================
--- linux-2.6.orig/fs/proc/base.c
+++ linux-2.6/fs/proc/base.c
@@ -97,6 +97,8 @@
 #include <linux/time_namespace.h>
 #include <linux/resctrl.h>
 #include <linux/cn_proc.h>
+#include <linux/prctl.h>
+#include <linux/task_isolation.h>
 #include <trace/events/oom.h>
 #include "internal.h"
 #include "fd.h"
@@ -665,6 +667,69 @@ static int proc_pid_syscall(struct seq_f
 }
 #endif /* CONFIG_HAVE_ARCH_TRACEHOOK */
 
+#ifdef CONFIG_TASK_ISOLATION
+
+struct qoptions {
+	unsigned long mask;
+	char *name;
+};
+
+static struct qoptions iopts[] = {
+	{ISOL_F_QUIESCE, "quiesce"},
+};
+#define ILEN (sizeof(iopts) / sizeof(struct qoptions))
+
+static struct qoptions qopts[] = {
+	{ISOL_F_QUIESCE_VMSTATS, "vmstat_sync"},
+};
+#define QLEN (sizeof(qopts) / sizeof(struct qoptions))
+
+static void show_isolation_state(struct seq_file *m,
+				 struct qoptions *iopt,
+				 int mask,
+				 const char *hdr)
+{
+	int i;
+
+	seq_printf(m, hdr);
+	for (i = 0; i < ILEN; i++) {
+		if (mask & iopt->mask)
+			seq_printf(m, "%s ", iopt->name);
+		iopt++;
+	}
+	if (mask == 0)
+		seq_printf(m, "none ");
+	seq_printf(m, "\n");
+}
+
+int proc_pid_task_isolation(struct seq_file *m, struct pid_namespace *ns,
+			    struct pid *pid, struct task_struct *t)
+{
+	int active_mask, quiesce_mask, conf_mask;
+	struct task_isol_info *task_isol_info;
+	struct inode *inode = m->private;
+	struct task_struct *task = get_proc_task(inode);
+
+	task_isol_info = t->task_isol_info;
+	if (!task_isol_info)
+		active_mask = quiesce_mask = conf_mask = 0;
+	else {
+		active_mask = task_isol_info->active_mask;
+		quiesce_mask = task_isol_info->quiesce_mask;
+		conf_mask = task_isol_info->conf_mask;
+	}
+
+	show_isolation_state(m, iopts, conf_mask, "Configured state: ");
+	show_isolation_state(m, iopts, active_mask, "Active state: ");
+	show_isolation_state(m, qopts, quiesce_mask, "Quiescing: ");
+
+	put_task_struct(task);
+
+	return 0;
+}
+
+#endif /* CONFIG_TASK_ISOLATION */
+
 /************************************************************************/
 /*                       Here the fs part begins                        */
 /************************************************************************/
@@ -3286,6 +3351,9 @@ static const struct pid_entry tgid_base_
 #ifdef CONFIG_SECCOMP_CACHE_DEBUG
 	ONE("seccomp_cache", S_IRUSR, proc_pid_seccomp_cache),
 #endif
+#ifdef CONFIG_TASK_ISOLATION
+	ONE("task_isolation", S_IRUSR, proc_pid_task_isolation),
+#endif
 };
 
 static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)