From deda2e81961e96be4f2c09328baca4710a2fd1a0 Mon Sep 17 00:00:00 2001 From: Jason Wessel Date: Mon, 9 Aug 2010 14:20:09 -0700 Subject: [PATCH] timekeeping: Fix overflow in rawtime tv_nsec on 32 bit archs The tv_nsec is a long and when added to the shifted interval it can wrap and become negative which later causes looping problems in the getrawmonotonic(). The edge case occurs when the system has slept for a short period of time of ~2 seconds. A trace printk of the values in this patch illustrate the problem: ftrace time stamp: log 43.716079: logarithmic_accumulation: raw: 3d0913 tv_nsec d687faa 43.718513: logarithmic_accumulation: raw: 3d0913 tv_nsec da588bd 43.722161: logarithmic_accumulation: raw: 3d0913 tv_nsec de291d0 46.349925: logarithmic_accumulation: raw: 7a122600 tv_nsec e1f9ae3 46.349930: logarithmic_accumulation: raw: 1e848980 tv_nsec 8831c0e3 The kernel starts looping at 46.349925 in the getrawmonotonic() due to the negative value from adding the raw value to tv_nsec. A simple solution is to accumulate into a u64, and then normalize it to a timespec_t. Signed-off-by: Jason Wessel [ Reworked variable names and simplified some of the code. - John ] Signed-off-by: John Stultz Cc: Thomas Gleixner Cc: H. Peter Anvin Signed-off-by: Linus Torvalds --- kernel/time/timekeeping.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index e14c839e9faa..e960d824263f 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -690,6 +690,7 @@ static void timekeeping_adjust(s64 offset) static cycle_t logarithmic_accumulation(cycle_t offset, int shift) { u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift; + u64 raw_nsecs; /* If the offset is smaller then a shifted interval, do nothing */ if (offset < timekeeper.cycle_interval<= NSEC_PER_SEC) { - raw_time.tv_nsec -= NSEC_PER_SEC; + /* Accumulate raw time */ + raw_nsecs = timekeeper.raw_interval << shift; + raw_nsecs += raw_time.tv_nsec; + while (raw_nsecs >= NSEC_PER_SEC) { + raw_nsecs -= NSEC_PER_SEC; raw_time.tv_sec++; } + raw_time.tv_nsec = raw_nsecs; /* Accumulate error between NTP and clock interval */ timekeeper.ntp_error += tick_length << shift; -- 2.20.1