time: Fix ktime_get_raw() incorrect base accumulation

In comqit fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time
handling"), the following code got mistakenly added to the update of the
raw timekeeper:

 /* Update the monotonic raw base */
 seconds = tk->raw_sec;
 nsec = (u32)(tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift);
 tk->tkr_raw.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);

Which adds the raw_sec value and the shifted down raw xtime_nsec to the
base value.

But the read function adds the shifted down tk->tkr_raw.xtime_nsec value
another time, The result of this is that ktime_get_raw() users (which are
all internal users) see the raw time move faster then it should (the rate
at which can vary with the current size of tkr_raw.xtime_nsec), which has
resulted in at least problems with graphics rendering performance.

The change tried to match the monotonic base update logic:

 seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
 nsec = (u32) tk->wall_to_monotonic.tv_nsec;
 tk->tkr_mono.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);

Which adds the wall_to_monotonic.tv_nsec value, but not the
tk->tkr_mono.xtime_nsec value to the base.

To fix this, simplify the tkr_raw.base accumulation to only accumulate the
raw_sec portion, and do not include the tkr_raw.xtime_nsec portion, which
will be added at read time.

Fixes: fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time handling")
Reported-and-tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Daniel Mentz <danielmentz@google.com>
Link: http://lkml.kernel.org/r/1503701824-1645-1-git-send-email-john.stultz@linaro.org

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index cedafa008de5a1196ff08a4422623893876b98b3..7e7e61c00d6145bb3de767e103f00552e3d4e362 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -637,9 +637,7 @@ static inline void tk_update_ktime_data(struct timekeeper *tk)
        tk->ktime_sec = seconds;
 
        /* Update the monotonic raw base */
-       seconds = tk->raw_sec;
-       nsec = (u32)(tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift);
-       tk->tkr_raw.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);
+       tk->tkr_raw.base = ns_to_ktime(tk->raw_sec * NSEC_PER_SEC);
 }
 
 /* must hold timekeeper_lock */