sched/clock: Fix early boot preempt assumption in __set_sched_clock_stable()

The more strict early boot preemption warnings found that
__set_sched_clock_stable() was incorrectly assuming we'd still be
running on a single CPU:

  BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
  caller is debug_smp_processor_id+0x1c/0x1e
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc2-00108-g1c3c5ea #1
  Call Trace:
   dump_stack+0x110/0x192
   check_preemption_disabled+0x10c/0x128
   ? set_debug_rodata+0x25/0x25
   debug_smp_processor_id+0x1c/0x1e
   sched_clock_init_late+0x27/0x87
  [...]

Fix it by disabling IRQs.

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: lkp@01.org
Cc: tipbuild@zytor.com
Link: http://lkml.kernel.org/r/20170524065202.v25vyu7pvba5mhpd@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 1a0d389d2f2b94bc3d221156e2c8de06cef1c436..ca0f8fc945c6d0891ffc58f54d2c08c271c21c65 100644 (file)
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -133,12 +133,19 @@ static void __scd_stamp(struct sched_clock_data *scd)
 
 static void __set_sched_clock_stable(void)
 {
-       struct sched_clock_data *scd = this_scd();
+       struct sched_clock_data *scd;
 
+       /*
+        * Since we're still unstable and the tick is already running, we have
+        * to disable IRQs in order to get a consistent scd->tick* reading.
+        */
+       local_irq_disable();
+       scd = this_scd();
        /*
         * Attempt to make the (initial) unstable->stable transition continuous.
         */
        __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
+       local_irq_enable();
 
        printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
                        scd->tick_gtod, __gtod_offset,