From 6855daa895c2913bbb755c0d2e256007057ae91a Mon Sep 17 00:00:00 2001
From: Muchun Song <songmuchun@bytedance.com>
Date: Mon, 20 Apr 2020 15:04:53 +0800
Subject: [PATCH] sched/cpuacct: Fix charge cpuacct.usage_sys

References: bnc#1155798 (CPU scheduler functional and performance backports)
Patch-mainline: v5.8-rc1
Git-commit: dbe9337109c2705f08e6a00392f991eb2d2570a5

The user_mode(task_pt_regs(tsk)) always return true for
user thread, and false for kernel thread. So it means that
the cpuacct.usage_sys is the time that kernel thread uses
not the time that thread uses in the kernel mode. We can
try get_irq_regs() first, if it is NULL, then we can fall
back to task_pt_regs().

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200420070453.76815-1-songmuchun@bytedance.com
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 kernel/sched/cpuacct.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 6448b0438ffb..941c28cf9738 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -5,6 +5,7 @@
  * Based on the work by Paul Menage (menage@google.com) and Balbir Singh
  * (balbir@in.ibm.com).
  */
+#include <asm/irq_regs.h>
 #include "sched.h"
 
 /* Time spent by the tasks of the CPU accounting group executing in ... */
@@ -339,7 +340,7 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
 	struct cpuacct *ca;
 	int index = CPUACCT_STAT_SYSTEM;
-	struct pt_regs *regs = task_pt_regs(tsk);
+	struct pt_regs *regs = get_irq_regs() ? : task_pt_regs(tsk);
 
 	if (regs && user_mode(regs))
 		index = CPUACCT_STAT_USER;