linux-kernel - [PATCH v2 2/2] sched: print parent comm in sched_show

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Date:   Tue, 31 Jan 2023 16:10:26 +0800
From:   Tio Zhang <tiozhang@...iglobal.com>
To:     <pmladek@...e.com>, <yu.c.chen@...el.com>
CC:     <juri.lelli@...hat.com>, <mingo@...hat.com>,
        <peterz@...radead.org>, <vincent.guittot@...aro.org>,
        <linux-kernel@...r.kernel.org>, <tiozhang@...iglobal.com>,
        <zyhtheonly@...il.com>, <zwp10758@...il.com>, <zyhtheonly@...h.net>
Subject: [PATCH v2 2/2] sched: print parent comm in sched_show_task()

Knowing who the parent is might be useful for debugging.
For example, we can sometimes resolve kernel hung tasks by stopping
the person who begins those hung tasks.
With the parent's name printed in sched_show_task(),
it might be helpful to let people know which "service" should be operated.
Also, we move the parent info to a following new line.
It would better solve the situation when the task
is not alive and we could not get information about the parent.

Signed-off-by: Tio Zhang <tiozhang@...iglobal.com>
---
 kernel/sched/core.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cb2aa2b54c7a..d8fd35684d6c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8853,7 +8853,6 @@ SYSCALL_DEFINE2(sched_rr_get_interval_time32, pid_t, pid,
 void sched_show_task(struct task_struct *p)
 {
 	unsigned long free = 0;
-	int ppid;
 
 	if (!try_get_task_stack(p))
 		return;
@@ -8865,14 +8864,19 @@ void sched_show_task(struct task_struct *p)
 #ifdef CONFIG_DEBUG_STACK_USAGE
 	free = stack_not_used(p);
 #endif
-	ppid = 0;
+
+	pr_cont(" stack:%-5lu pid:%-5d flags:0x%08lx\n",
+		free, task_pid_nr(p), read_task_thread_flags(p));
+
 	rcu_read_lock();
-	if (pid_alive(p))
-		ppid = task_pid_nr(rcu_dereference(p->real_parent));
+	if (pid_alive(p)) {
+		struct task_struct *parent = rcu_dereference(p->real_parent);
+
+		pr_info("parent:%-15.15s ppid:%-6d", parent->comm, task_pid_nr(parent));
+	} else {
+		pr_info("parent:unknown         ppid:<NULL>\n");
+	}
 	rcu_read_unlock();
-	pr_cont(" stack:%-5lu pid:%-5d ppid:%-6d flags:0x%08lx\n",
-		free, task_pid_nr(p), ppid,
-		read_task_thread_flags(p));
 
 	print_worker_info(KERN_INFO, p);
 	print_stop_info(KERN_INFO, p);
-- 
2.17.1