diff options
| author | Tony Luck <tony.luck@intel.com> | 2014-07-18 11:43:01 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-07-31 12:52:55 -0700 |
| commit | b8dea936e3c13157355e424c496ad25f3f71cf64 (patch) | |
| tree | efb63447eb5966a97ea1c8a62e4d10e9f8c5cb15 /kernel | |
| parent | d98c246a64929965ebcd946344548ae6c00fa4aa (diff) | |
tracing: Fix wraparound problems in "uptime" trace clock
commit 58d4e21e50ff3cc57910a8abc20d7e14375d2f61 upstream.
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
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/trace.c | 2 | ||||
| -rw-r--r-- | kernel/trace/trace_clock.c | 9 |
2 files changed, 6 insertions, 5 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 7e259b2bdf44..71136720ffa1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -811,7 +811,7 @@ static struct { { trace_clock_local, "local", 1 }, { trace_clock_global, "global", 1 }, { trace_clock_counter, "counter", 0 }, - { trace_clock_jiffies, "uptime", 1 }, + { trace_clock_jiffies, "uptime", 0 }, { trace_clock, "perf", 1 }, ARCH_TRACE_CLOCKS }; diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c index 26dc348332b7..57b67b1f24d1 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); } /* |