Commit 0e4097c3 authored Jul 09, 2017 by Wanpeng Li Committed by Ingo Molnar Jul 14, 2017

sched/cputime: Don't use smp_processor_id() in preemptible context



Recent kernels trigger this warning:

 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()
  debug_smp_processor_id()
  vtime_delta()
  task_cputime()
  thread_group_cputime()
  thread_group_cputime_adjusted()
  wait_consider_task()
  do_wait()
  SYSC_wait4()
  do_syscall_64()
  entry_SYSCALL64_slow_path()

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() with sched_clock() to
avoid calling smp_processor_id() in a preemptible context.

Reported-by: Xiaolong Ye <xiaolong.ye@intel.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1499586028-7402-1-git-send-email-wanpeng.li@hotmail.com


[ Prettified the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 242fc352

kernel/sched/cputime.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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);
		}

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