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author | John Stultz <john.stultz@linaro.org> | 2015-03-11 21:16:34 -0700 |
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committer | Ingo Molnar <mingo@kernel.org> | 2015-03-13 08:07:05 +0100 |
commit | 057b87e3161d1194a095718f9918c01b2c389e74 (patch) | |
tree | 8f6b79b5f9d6c12b8a53148e04961081eb9f3243 /kernel/time | |
parent | a558cd021d83b65c47ee5b9bec1fcfe5298a769f (diff) | |
download | op-kernel-dev-057b87e3161d1194a095718f9918c01b2c389e74.zip op-kernel-dev-057b87e3161d1194a095718f9918c01b2c389e74.tar.gz |
timekeeping: Try to catch clocksource delta underflows
In the case where there is a broken clocksource
where there are multiple actual clocks that
aren't perfectly aligned, we may see small "negative"
deltas when we subtract 'now' from 'cycle_last'.
The values are actually negative with respect to the
clocksource mask value, not necessarily negative
if cast to a s64, but we can check by checking the
delta to see if it is a small (relative to the mask)
negative value (again negative relative to the mask).
If so, we assume we jumped backwards somehow and
instead use zero for our delta.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-7-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/time')
-rw-r--r-- | kernel/time/timekeeping.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 657414c..187149b 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -148,6 +148,13 @@ static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr) /* calculate the delta since the last update_wall_time */ delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask); + /* + * Try to catch underflows by checking if we are seeing small + * mask-relative negative values. + */ + if (unlikely((~delta & tkr->mask) < (tkr->mask >> 3))) + delta = 0; + /* Cap delta value to the max_cycles values to avoid mult overflows */ if (unlikely(delta > tkr->clock->max_cycles)) delta = tkr->clock->max_cycles; |