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authorJohn Stultz <john.stultz@linaro.org>2015-09-09 16:07:30 -0700
committerIngo Molnar <mingo@kernel.org>2015-09-13 10:30:47 +0200
commit2619d7e9c92d524cb155ec89fd72875321512e5b (patch)
tree90ec69c5e8b7604b184fe385392a947e094781d3 /kernel/time
parent6ff33f3902c3b1c5d0db6b1e2c70b6d76fba357f (diff)
downloadlinux-2619d7e9c92d524cb155ec89fd72875321512e5b.tar.bz2
time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64()
The internal clocksteering done for fine-grained error correction uses a logarithmic approximation, so any time adjtimex() adjusts the clock steering, timekeeping_freqadjust() quickly approximates the correct clock frequency over a series of ticks. Unfortunately, the logic in timekeeping_freqadjust(), introduced in commit: dc491596f639 ("timekeeping: Rework frequency adjustments to work better w/ nohz") used the abs() function with a s64 error value to calculate the size of the approximated adjustment to be made. Per include/linux/kernel.h: "abs() should not be used for 64-bit types (s64, u64, long long) - use abs64()". Thus on 32-bit platforms, this resulted in the clocksteering to take a quite dampended random walk trying to converge on the proper frequency, which caused the adjustments to be made much slower then intended (most easily observed when large adjustments are made). This patch fixes the issue by using abs64() instead. Reported-by: Nuno Gonçalves <nunojpg@gmail.com> Tested-by: Nuno Goncalves <nunojpg@gmail.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: <stable@vger.kernel.org> # v3.17+ Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Miroslav Lichvar <mlichvar@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1441840051-20244-1-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.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index f6ee2e6b6f5d..3739ac6aa473 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1614,7 +1614,7 @@ static __always_inline void timekeeping_freqadjust(struct timekeeper *tk,
negative = (tick_error < 0);
/* Sort out the magnitude of the correction */
- tick_error = abs(tick_error);
+ tick_error = abs64(tick_error);
for (adj = 0; tick_error > interval; adj++)
tick_error >>= 1;