Merge tag 'trace-fixes-v3.16-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull trace fix from Steven Rostedt:
 "Tony Luck found that using the "uptime" trace clock that uses jiffies
  as a counter was converted to nanoseconds (silly), and after 1 hour 11
  minutes and 34 seconds, this monotonic clock would wrap, causing havoc
  with the tracing system and making the clock useless.

  He converted that clock to use jiffies_64 and made it into a counter
  instead of nanosecond conversions, and displayed the clock with the
  straight jiffy count, which works much better than it did in the past"

* tag 'trace-fixes-v3.16-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Fix wraparound problems in "uptime" trace clock

2 files changed, 6 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index bda9621638cc..291397e66669 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -823,7 +823,7 @@ 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);
 }
 
 /*