From 45aea321678856687927c53972321ebfab77759a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra 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 Signed-off-by: Peter Zijlstra (Intel) Acked-by: Thomas Gleixner Cc: Greg Kroah-Hartman Cc: Linus Torvalds Cc: Mark Rutland Cc: Peter Zijlstra Cc: Steven Rostedt 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 --- kernel/sched/clock.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index 1a0d389d2f2b..ca0f8fc945c6 100644 --- 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, -- 2.20.1