Commit efd39f77 authored by Tony Luck's avatar Tony Luck Committed by Greg Kroah-Hartman

tracing: Fix wraparound problems in "uptime" trace clock

commit 58d4e21e50ff3cc57910a8abc20d7e14375d2f61 upstream.

The "uptime" trace clock added in:

    commit 8aacf017
    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: 8aacf017 "tracing: Add "uptime" trace clock that uses jiffies"
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent cebdb6fa
......@@ -741,7 +741,7 @@ 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
};
......
......@@ -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);
}
/*
......
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