linux-kernel - [tip:core/printk] timekeeping: Make fast accessors return 0 before timekeeping is initialized

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Message-ID: <tip-5df32107f609c1f621bcdac0a685c23677ef671e@git.kernel.org>
Date:   Mon, 25 Sep 2017 12:18:44 -0700
From:   tip-bot for Prarit Bhargava <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        prarit@...hat.com, sboyd@...eaurora.org, hpa@...or.com,
        mingo@...nel.org, john.stultz@...aro.org, peterz@...radead.org
Subject: [tip:core/printk] timekeeping: Make fast accessors return 0 before
 timekeeping is initialized

Commit-ID:  5df32107f609c1f621bcdac0a685c23677ef671e
Gitweb:     http://git.kernel.org/tip/5df32107f609c1f621bcdac0a685c23677ef671e
Author:     Prarit Bhargava <prarit@...hat.com>
AuthorDate: Mon, 28 Aug 2017 08:21:53 -0400
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon, 25 Sep 2017 21:05:59 +0200

timekeeping: Make fast accessors return 0 before timekeeping is initialized

printk timestamps will be extended to include mono and boot time by using
the fast timekeeping accessors ktime_get_mono|boot_fast_ns().  The
functions can return garbage before timekeeping is initialized resulting in
garbage timestamps.

Initialize the fast timekeepers with dummy clocks which guarantee a 0
readout up to timekeeping_init().

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Prarit Bhargava <prarit@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Stephen Boyd <sboyd@...eaurora.org>
Cc: John Stultz <john.stultz@...aro.org>
Link: http://lkml.kernel.org/r/1503922914-10660-2-git-send-email-prarit@redhat.com

---
 kernel/time/timekeeping.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 2cafb49..6a92794 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -60,8 +60,27 @@ struct tk_fast {
 	struct tk_read_base	base[2];
 };
 
-static struct tk_fast tk_fast_mono ____cacheline_aligned;
-static struct tk_fast tk_fast_raw  ____cacheline_aligned;
+/* Suspend-time cycles value for halted fast timekeeper. */
+static u64 cycles_at_suspend;
+
+static u64 dummy_clock_read(struct clocksource *cs)
+{
+	return cycles_at_suspend;
+}
+
+static struct clocksource dummy_clock = {
+	.read = dummy_clock_read,
+};
+
+static struct tk_fast tk_fast_mono ____cacheline_aligned = {
+	.base[0] = { .clock = &dummy_clock, },
+	.base[1] = { .clock = &dummy_clock, },
+};
+
+static struct tk_fast tk_fast_raw  ____cacheline_aligned = {
+	.base[0] = { .clock = &dummy_clock, },
+	.base[1] = { .clock = &dummy_clock, },
+};
 
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
@@ -477,18 +496,6 @@ u64 notrace ktime_get_boot_fast_ns(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);
 
-/* Suspend-time cycles value for halted fast timekeeper. */
-static u64 cycles_at_suspend;
-
-static u64 dummy_clock_read(struct clocksource *cs)
-{
-	return cycles_at_suspend;
-}
-
-static struct clocksource dummy_clock = {
-	.read = dummy_clock_read,
-};
-
 /**
  * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
  * @tk: Timekeeper to snapshot.