| From: Peter Zijlstra <peterz@infradead.org> |
| Date: Wed, 24 May 2017 08:52:02 +0200 |
| Subject: [PATCH] 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> |
| --- |
| kernel/sched/clock.c | 9 ++++++++- |
| 1 file changed, 8 insertions(+), 1 deletion(-) |
| |
| --- a/kernel/sched/clock.c |
| +++ b/kernel/sched/clock.c |
| @@ -126,12 +126,19 @@ int sched_clock_stable(void) |
| |
| 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, |