Patch "sched/cputime: Don't use smp_processor_id() in preemptible context" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sched-cputime-don-t-use-smp_processor_id-in-preemptible-context.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Wanpeng Li <[email protected]>
Date: Sun, 9 Jul 2017 00:40:28 -0700
Subject: sched/cputime: Don't use smp_processor_id() in preemptible context

From: Wanpeng Li <[email protected]>

commit 0e4097c3354e2f5a5ad8affd9dc7f7f7d00bb6b9 upstream.

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.

---
 kernel/sched/cputime.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -683,7 +683,7 @@ static u64 vtime_delta(struct vtime *vti
 {
 	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_
 
 	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
 	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);
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/sched-cputime-don-t-use-smp_processor_id-in-preemptible-context.patch queue-4.12/sched-cputime-accumulate-vtime-on-top-of-nsec-clocksource.patch