[PATCH] RFC: hung task: Check specific tasks for long uninterruptible sleep state

[Imran Khan]

khungtask by default monitors either all tasks or no tasks at all
for long unterruptible sleeps.
For Android like environments this arrangement is not optimal because
on one hand it may be permissible to have some background(bg) task
in uninterruptible sleep state for long duration while on the other
hand it may not be permissible to have some foreground(fg) task like
surfaceflinger in uninterruptible sleep state for long duration.
So it would be good to have some arrangement so that few specified tasks
can be monitored by khungtaskd, on a need basis.
This change introduces a sysctl option, /proc/sys/kernel/
hung_task_check_selected, to enable monitoring of selected tasks using
khungtask daemon. If this sysctl option is enabled then only the tasks
specified in /proc/hung_task_monitor_list are monitored otherwise all
tasks are monitored, just like the default case.

Signed-off-by: Imran Khan <kimran@xxxxxxxxxxxxxx>
---
 include/linux/sched/sysctl.h |   1 +
 kernel/hung_task.c           | 121 ++++++++++++++++++++++++++++++++++++++++++-
 kernel/sysctl.c              |   8 +++
 3 files changed, 128 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index 0f5ecd4..05892f1 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -10,6 +10,7 @@
 extern unsigned int  sysctl_hung_task_panic;
 extern unsigned long sysctl_hung_task_timeout_secs;
 extern int sysctl_hung_task_warnings;
+extern int sysctl_hung_task_check_selected;
 extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 					 void __user *buffer,
 					 size_t *lenp, loff_t *ppos);
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 751593e..49f13fb 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -16,12 +16,28 @@
 #include <linux/export.h>
 #include <linux/sysctl.h>
 #include <linux/utsname.h>
+#include <linux/uaccess.h>
+#include <linux/slab.h>
+#include <linux/proc_fs.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/debug.h>
 
 #include <trace/events/sched.h>
 
 /*
+ * Hung task that needs monitoring
+ */
+struct hung_task {
+	struct list_head list;
+	char comm[TASK_COMM_LEN];
+};
+
+static struct hung_task	*monitor_list;
+int sysctl_hung_task_check_selected;
+
+
+
+/*
  * The number of tasks checked:
  */
 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
@@ -76,6 +92,92 @@ static int __init hung_task_panic_setup(char *str)
 	.notifier_call = hung_task_panic,
 };
 
+static void hung_task_monitor_setup(void)
+{
+	monitor_list = kmalloc(sizeof(*monitor_list), GFP_KERNEL);
+	if (monitor_list) {
+		INIT_LIST_HEAD(&monitor_list->list);
+		memset(monitor_list->comm, 0, TASK_COMM_LEN);
+	}
+}
+
+
+static  int hung_task_info_show(struct seq_file *m, void *v)
+{
+	struct hung_task *ht;
+
+	ht = list_entry(v, struct hung_task, list);
+	seq_puts(m, ht->comm);
+
+	return 0;
+}
+
+static void *hung_task_info_start(struct seq_file *m, loff_t *pos)
+{
+	return seq_list_start_head(&monitor_list->list, *pos);
+}
+
+static void *hung_task_info_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	return seq_list_next(v, &monitor_list->list, pos);
+}
+
+static void hung_task_info_stop(struct seq_file *m, void *v)
+{
+}
+
+const struct seq_operations hung_task_info_op = {
+	.start	= hung_task_info_start,
+	.next	= hung_task_info_next,
+	.stop	= hung_task_info_stop,
+	.show	= hung_task_info_show
+};
+
+static int hung_task_info_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &hung_task_info_op);
+}
+
+static ssize_t
+hung_task_info_write(struct file *file, const char __user *buf, size_t count,
+	     loff_t *offs)
+{
+	struct task_struct *g, *t;
+	struct hung_task *ht = kmalloc(sizeof(*ht), GFP_KERNEL);
+
+	if (!ht)
+		return -ENOMEM;
+
+	if (copy_from_user(ht->comm, buf, count))
+		return -EFAULT;
+	ht->comm[count] = '\0';
+
+	for_each_process_thread(g, t) {
+		if (!strncmp(t->comm, ht->comm, strlen(t->comm))) {
+			list_add_tail(&ht->list, &monitor_list->list);
+			return count;
+		}
+	}
+
+	pr_err("Non-existing task: %s can't be monitored\n", ht->comm);
+	return count;
+}
+
+static const struct file_operations hung_task_info_operations = {
+	.open		= hung_task_info_open,
+	.read		= seq_read,
+	.write		= hung_task_info_write,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static int __init proc_hung_task_info_init(void)
+{
+	proc_create("hung_task_monitor_list", 0644, NULL,
+		    &hung_task_info_operations);
+	return 0;
+}
+
 static void check_hung_task(struct task_struct *t, unsigned long timeout)
 {
 	unsigned long switch_count = t->nvcsw + t->nivcsw;
@@ -167,6 +269,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 	int max_count = sysctl_hung_task_check_count;
 	int batch_count = HUNG_TASK_BATCHING;
 	struct task_struct *g, *t;
+	struct hung_task *ht, *tmp;
 
 	/*
 	 * If the system crashed already then all bets are off,
@@ -186,9 +289,21 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 				goto unlock;
 		}
 		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
-		if (t->state == TASK_UNINTERRUPTIBLE)
-			check_hung_task(t, timeout);
+		if (t->state == TASK_UNINTERRUPTIBLE) {
+			if (sysctl_hung_task_check_selected) {
+				list_for_each_entry_safe(ht, tmp,
+							 &monitor_list->list,
+							 list)
+					if (!strncmp(ht->comm, t->comm,
+					    strlen(t->comm)))
+					/* Task belongs to the selected group */
+						check_hung_task(t, timeout);
+			} else {
+				check_hung_task(t, timeout);
+			}
+		}
 	}
+
  unlock:
 	rcu_read_unlock();
 	if (hung_task_show_lock)
@@ -259,6 +374,8 @@ static int watchdog(void *dummy)
 static int __init hung_task_init(void)
 {
 	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
+	hung_task_monitor_setup();
+	proc_hung_task_info_init();
 	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 
 	return 0;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6648fbb..ab45774 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1096,6 +1096,14 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &neg_one,
 	},
+	{
+		.procname	= "hung_task_check_selected",
+		.data		= &sysctl_hung_task_check_selected,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &neg_one,
+	},
 #endif
 #ifdef CONFIG_RT_MUTEXES
 	{
-- 
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