On Thu, Jul 19, 2018 at 04:55:42PM -0400, Pavel Tatashin wrote: > diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c > index 0e9dbb2d9aea..422cd63f8f17 100644 > --- a/kernel/sched/clock.c > +++ b/kernel/sched/clock.c > @@ -202,7 +202,25 @@ static void __sched_clock_gtod_offset(void) > > void __init sched_clock_init(void) > { > + unsigned long flags; > + > + /* > + * Set __gtod_offset such that once we mark sched_clock_running, > + * sched_clock_tick() continues where sched_clock() left off. > + * > + * Even if TSC is buggered, we're still UP at this point so it > + * can't really be out of sync. > + */ > + local_irq_save(flags); > + __sched_clock_gtod_offset(); > + local_irq_restore(flags); > + > sched_clock_running = 1; > + > + /* Now that sched_clock_running is set adjust scd */ > + local_irq_save(flags); > + sched_clock_tick(); > + local_irq_restore(flags); > } Sorry, that's still wrong. Because the moment you enable sched_clock_running we need to have everything set-up for it to run. The above looks double weird because you could've just done that =1 under the same IRQ-disable section and it would've mostly been OK (except for NMIs). But the reason it's weird like that is because you're going to change it into a static key later on. The below cures things. --- Subject: sched/clock: Close a hole in sched_clock_init() All data required for the 'unstable' sched_clock must be set-up _before_ enabling it -- setting sched_clock_running. This includes the __gtod_offset but also a recent scd stamp. Make the gtod-offset update also set the csd stamp -- it requires the same two clock reads _anyway_. This doesn't hurt in the sched_clock_tick_stable() case and ensures sched_clock_init() gets everything set-up before use. Also switch to unconditional IRQ-disable/enable because the static key stuff already requires this is not ran with IRQs disabled. Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> --- kernel/sched/clock.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index c5c47ad3f386..811a39aca1ce 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -197,13 +197,14 @@ void clear_sched_clock_stable(void) static void __sched_clock_gtod_offset(void) { - __gtod_offset = (sched_clock() + __sched_clock_offset) - ktime_get_ns(); + struct sched_clock_data *scd = this_scd(); + + __scd_stamp(scd); + __gtod_offset = (scd->tick_raw + __sched_clock_offset) - scd->tick_gtod; } void __init sched_clock_init(void) { - unsigned long flags; - /* * Set __gtod_offset such that once we mark sched_clock_running, * sched_clock_tick() continues where sched_clock() left off. @@ -211,16 +212,11 @@ void __init sched_clock_init(void) * Even if TSC is buggered, we're still UP at this point so it * can't really be out of sync. */ - local_irq_save(flags); + local_irq_disable(); __sched_clock_gtod_offset(); - local_irq_restore(flags); + local_irq_enable(); static_branch_inc(&sched_clock_running); - - /* Now that sched_clock_running is set adjust scd */ - local_irq_save(flags); - sched_clock_tick(); - local_irq_restore(flags); } /* * We run this as late_initcall() such that it runs after all built-in drivers, -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html