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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@infradead.org>
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/1503922914-10660-2-git-send-email-prarit@redhat.com
This commit is contained in:
Prarit Bhargava 2017-08-28 08:21:53 -04:00 committed by Thomas Gleixner
parent e19b205be4
commit 5df32107f6
1 changed files with 21 additions and 14 deletions
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35
kernel/time/timekeeping.c
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@ -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.