[PATCH] kernel/hung_task: print real_parent->comm, pid in check_hung_task

[Tio Zhang <tiozhang@didiglobal.com>]

We can avoid a hung task by fixing the process who causes it.
But sometimes it is difficult to find out which service 
the bad process belongs to by only knowing its pid and comm.
Since userspace tools to learn who launches the bad process
do not always work when we get a hung task, 
it is helpful printing the parent by kernel.

Signed-off-by: Tio Zhang <tiozhang@didiglobal.com>
---
 kernel/hung_task.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index c71889f3f3fc..33543d27bd5c 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -89,6 +89,7 @@ static struct notifier_block panic_block = {
 
 static void check_hung_task(struct task_struct *t, unsigned long timeout)
 {
+	struct task_struct *p = t->real_parent;
 	unsigned long switch_count = t->nvcsw + t->nivcsw;
 
 	/*
@@ -129,8 +130,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 	if (sysctl_hung_task_warnings) {
 		if (sysctl_hung_task_warnings > 0)
 			sysctl_hung_task_warnings--;
-		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
-		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
+		pr_err("INFO: task %s:%d, parent %s:%d blocked for more than %ld seconds.\n",
+		       t->comm, t->pid, p->comm, p->pid, (jiffies - t->last_switch_time) / HZ);
 		pr_err("      %s %s %.*s\n",
 			print_tainted(), init_utsname()->release,
 			(int)strcspn(init_utsname()->version, " "),
-- 
2.17.1