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Subject[tip:x86/timers] sched/clock: Close a hole in sched_clock_init()
Commit-ID:  9407f5a7ee77c631d1e100436132437cf6237e45
Gitweb: https://git.kernel.org/tip/9407f5a7ee77c631d1e100436132437cf6237e45
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 20 Jul 2018 10:09:11 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 20 Jul 2018 11:58:00 +0200

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.

Fixes: 857baa87b642 ("sched/clock: Enable sched clock early")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180720080911.GM2494@hirez.programming.kicks-ass.net
---
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,
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