On Fri, 18 Jul 2014 11:43:01 -0700 Tony Luck <[email protected]> wrote:
> The "uptime" tracer 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). > Do you think this is worthy of stable and 3.16 material? -- Steve > Signed-off-by: Tony Luck <[email protected]> > --- > kernel/trace/trace.c | 2 +- > 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 384ede311717..eb7d56480545 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -809,7 +809,7 @@ 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); > } > > /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
