linux-kernel - [PATCH] sched/cputime: Fix using smp_processor

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Date:   Thu,  6 Jul 2017 20:18:41 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...hat.com>
Subject: [PATCH] sched/cputime: Fix using smp_processor_id() in preemptible

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

 BUG: using smp_processor_id() in preemptible [00000000] code: 99-trinity/181
 caller is debug_smp_processor_id+0x17/0x19
 CPU: 0 PID: 181 Comm: 99-trinity Not tainted 4.12.0-01059-g2a42eb9 #1
 Call Trace:
  dump_stack+0x82/0xb8
  check_preemption_disabled+0xd1/0xe3
  debug_smp_processor_id+0x17/0x19
  vtime_delta+0xd/0x2c
  task_cputime+0x89/0xdb
  thread_group_cputime+0x11b/0x1ed
  thread_group_cputime_adjusted+0x1f/0x47
  wait_consider_task+0x2a9/0xaf9
  ? lock_acquire+0x97/0xa4
  do_wait+0xdf/0x1f4
  SYSC_wait4+0x8e/0xb5
  ? list_add+0x34/0x34
  SyS_wait4+0x9/0xb
  do_syscall_64+0x70/0x82
  entry_SYSCALL64_slow_path+0x25/0x25

As Frederic pointed out:

| Although those sched_clock_cpu() things seem to only matter when the
| sched_clock() is unstable. And that stability is a condition for nohz_full
| to work anyway. So probably sched_clock() alone would be enough.

This patch fixes it by replacing sched_clock_cpu() in vtime_delta() by 
sched_clock() to avoid to call smp_processor_id() in preemptible context.

Reported-by: Xiaolong Ye <xiaolong.ye@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 kernel/sched/cputime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 6e3ea4a..d86b94e 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -683,7 +683,7 @@ static u64 vtime_delta(struct vtime *vtime)
 {
 	unsigned long long clock;

-	clock = sched_clock_cpu(smp_processor_id());
+	clock = sched_clock();
 	if (clock < vtime->starttime)
 		return 0;

-- 
2.7.4