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authorTony Luck <tony.luck@intel.com>2014-07-18 18:43:01 (GMT)
committerSteven Rostedt <rostedt@goodmis.org>2014-07-21 13:56:12 (GMT)
commit58d4e21e50ff3cc57910a8abc20d7e14375d2f61 (patch)
tree613b543c7ac7983d130d6e20880d6590ff06a893 /kernel/trace/trace_clock.c
parent9a3c4145af32125c5ee39c0272662b47307a8323 (diff)
downloadlinux-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.c9
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);
}
/*