sched/clock: Close a hole in sched_clock_init()

Peter Zijlstra · KAGA-KOKO · commit 9407f5a7ee77 · 2018-07-20T11:58:00.000+02:00
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: 857baa8 ("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
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
@@ -197,30 +197,26 @@ 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.
 	 *
 	 * 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,
