This is a note to let you know that I've just added the patch titled
tracing: Fix wraparound problems in "uptime" trace clock
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-fix-wraparound-problems-in-uptime-trace-clock.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 58d4e21e50ff3cc57910a8abc20d7e14375d2f61 Mon Sep 17 00:00:00 2001
From: Tony Luck <tony.luck@xxxxxxxxx>
Date: Fri, 18 Jul 2014 11:43:01 -0700
Subject: tracing: Fix wraparound problems in "uptime" trace clock
From: Tony Luck <tony.luck@xxxxxxxxx>
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@xxxxxxxxx
Fixes: 8aacf017b065 "tracing: Add "uptime" trace clock that uses jiffies"
Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/trace.c | 2 +-
kernel/trace/trace_clock.c | 9 +++++----
2 files changed, 6 insertions(+), 5 deletions(-)
--- 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
};
--- 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);
}
/*
Patches currently in stable-queue which might be from tony.luck@xxxxxxxxx are
queue-3.14/tracing-fix-wraparound-problems-in-uptime-trace-clock.patch
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