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| author | Tony Luck <tony.luck@intel.com> | 2014-07-18 18:43:01 (GMT) |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2014-07-21 13:56:12 (GMT) |
| commit | 58d4e21e50ff3cc57910a8abc20d7e14375d2f61 (patch) | |
| tree | 613b543c7ac7983d130d6e20880d6590ff06a893 /kernel/trace/trace_clock.c | |
| parent | 9a3c4145af32125c5ee39c0272662b47307a8323 (diff) | |
| download | linux-58d4e21e50ff3cc57910a8abc20d7e14375d2f61.tar.xz | |
tracing: Fix wraparound problems in "uptime" trace clock
The "uptime" trace clock added in:
commit 8aacf017b065a805d27467843490c976835eb4a5
tracing: Add "uptime" trace clock that uses jiffies
has wraparound problems when the system has been up more
than 1 hour 11 minutes and 34 seconds. It converts jiffies
to nanoseconds using:
(u64)jiffies_to_usecs(jiffy) * 1000ULL
but since jiffies_to_usecs() only returns a 32-bit value, it
truncates at 2^32 microseconds. An additional problem on 32-bit
systems is that the argument is "unsigned long", so fixing the
return value only helps until 2^32 jiffies (49.7 days on a HZ=1000
system).
Avoid these problems by using jiffies_64 as our basis, and
not converting to nanoseconds (we do convert to clock_t because
user facing API must not be dependent on internal kernel
HZ values).
Link: http://lkml.kernel.org/p/99d63c5bfe9b320a3b428d773825a37095bf6a51.1405708254.git.tony.luck@intel.com
Cc: stable@vger.kernel.org # 3.10+
Fixes: 8aacf017b065 "tracing: Add "uptime" trace clock that uses jiffies"
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace_clock.c')
| -rw-r--r-- | kernel/trace/trace_clock.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c index 26dc348..57b67b1 100644 --- a/kernel/trace/trace_clock.c +++ b/kernel/trace/trace_clock.c @@ -59,13 +59,14 @@ u64 notrace trace_clock(void) /* * trace_jiffy_clock(): Simply use jiffies as a clock counter. + * Note that this use of jiffies_64 is not completely safe on + * 32-bit systems. But the window is tiny, and the effect if + * we are affected is that we will have an obviously bogus + * timestamp on a trace event - i.e. not life threatening. */ u64 notrace trace_clock_jiffies(void) { - u64 jiffy = jiffies - INITIAL_JIFFIES; - - /* Return nsecs */ - return (u64)jiffies_to_usecs(jiffy) * 1000ULL; + return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES); } /* |