From 373c96e1499c7e450e6723611cd8100e00b4292b Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Wed, 29 Sep 2021 15:02:15 -0700
Subject: [PATCH] proc: Use task_is_running() for wchan in /proc/$pid/stat

References: bsc#1189999 (Scheduler functional and performance backports)
Patch-mainline: v5.16-rc1
Git-commit: 4e046156792c26bef8a4e30be711777fc8578257

The implementations of get_wchan() can be expensive. The only information
imparted here is whether or not a process is currently blocked in the
scheduler (and even this doesn't need to be exact). Avoid doing the
heavy lifting of stack walking and just report that information by using
task_is_running().

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211008111626.211281780@infradead.org
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 fs/proc/array.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index ee0ce8cecc4a..6817639baa0f 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -551,7 +551,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 	}
 
 	if (permitted && (!whole || num_threads < 2))
-		wchan = get_wchan(task);
+		wchan = !task_is_running(task);
 	if (!whole) {
 		min_flt = task->min_flt;
 		maj_flt = task->maj_flt;
@@ -616,10 +616,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 	 *
 	 * This works with older implementations of procps as well.
 	 */
-	if (wchan)
-		seq_puts(m, " 1");
-	else
-		seq_puts(m, " 0");
+	seq_put_decimal_ull(m, " ", wchan);
 
 	seq_put_decimal_ull(m, " ", 0);
 	seq_put_decimal_ull(m, " ", 0);