linux-kernel - [PATCH tip/core/rcu 5/5] EXP: sched/cputime: Fix using smp_processor

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Message-Id: <1500933497-12612-5-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Mon, 24 Jul 2017 14:58:17 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 5/5] EXP: 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>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/sched/cputime.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 6e3ea4ac1bda..14d2dbf97c53 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;

@@ -814,7 +814,7 @@ void arch_vtime_task_switch(struct task_struct *prev)

 	write_seqcount_begin(&vtime->seqcount);
 	vtime->state = VTIME_SYS;
-	vtime->starttime = sched_clock_cpu(smp_processor_id());
+	vtime->starttime = sched_clock();
 	write_seqcount_end(&vtime->seqcount);
 }

@@ -826,7 +826,7 @@ void vtime_init_idle(struct task_struct *t, int cpu)
 	local_irq_save(flags);
 	write_seqcount_begin(&vtime->seqcount);
 	vtime->state = VTIME_SYS;
-	vtime->starttime = sched_clock_cpu(cpu);
+	vtime->starttime = sched_clock();
 	write_seqcount_end(&vtime->seqcount);
 	local_irq_restore(flags);
 }
-- 
2.5.2