linux-kernel - [PATCH] sched/fair: Update rq clock before changing a task's CPU affinity

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Date:   Tue, 21 Feb 2017 23:52:55 -0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Wanpeng Li <wanpeng.li@...mail.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: [PATCH] sched/fair: Update rq clock before changing a task's CPU affinity

From: Wanpeng Li <wanpeng.li@...mail.com>

 ------------[ cut here ]------------
 WARNING: CPU: 6 PID: 81 at kernel/sched/sched.h:812 set_next_entity+0x11d/0x380
 rq->clock_update_flags < RQCF_ACT_SKIP
 CPU: 6 PID: 81 Comm: torture_shuffle Not tainted 4.10.0+ #1
 Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS FBKTC1AUS 02/16/2016
 Call Trace:
  dump_stack+0x85/0xc2
  __warn+0xcb/0xf0
  warn_slowpath_fmt+0x5f/0x80
  set_next_entity+0x11d/0x380
  set_curr_task_fair+0x2b/0x60
  do_set_cpus_allowed+0x139/0x180
  __set_cpus_allowed_ptr+0x113/0x260
  set_cpus_allowed_ptr+0x10/0x20
  torture_shuffle+0xfd/0x180
  kthread+0x10f/0x150
  ? torture_shutdown_init+0x60/0x60
  ? kthread_create_on_node+0x60/0x60
  ret_from_fork+0x31/0x40
 ---[ end trace dd94d92344cea9c6 ]---

This is triggered during boot when CONFIG_SCHED_DEBUG is enabled. The 
task is running && !queued, so there is no rq clock update before calling 
set_curr_task.

This patch fixes it by updating rq clock after holding rq->lock/pi_lock 
just as what other dequeue + put_prev + enqueue + set_curr story does.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Matt Fleming <matt@...eblueprint.co.uk>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 34e2291..2c51bdf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1087,6 +1087,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 	int ret = 0;
 
 	rq = task_rq_lock(p, &rf);
+	update_rq_clock(rq);
 
 	if (p->flags & PF_KTHREAD) {
 		/*
-- 
2.7.4