2015-04-30 14:36:43

by Jerry Snitselaar

Subject: [PATCH] tracing: Export tracing clock functions

Critical tracepoint hooks shoud never call anything that takes a lock,
so they are unable to call getrawmonotonic() or ktime_get().

Export the rest of the tracing clock functions so can be used in
tracepoint hooks.

Cc: Steven Rostedt <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Jerry Snitselaar <[email protected]>
---
kernel/trace/trace_clock.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index 57b67b1..0f06532 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -56,6 +56,7 @@ u64 notrace trace_clock(void)
{
return local_clock();
}
+EXPORT_SYMBOL_GPL(trace_clock);

/*
* trace_jiffy_clock(): Simply use jiffies as a clock counter.
@@ -68,6 +69,7 @@ u64 notrace trace_clock_jiffies(void)
{
return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
}
+EXPORT_SYMBOL_GPL(trace_clock_jiffies);

/*
* trace_clock_global(): special globally coherent trace clock
@@ -123,6 +125,7 @@ u64 notrace trace_clock_global(void)

return now;
}
+EXPORT_SYMBOL_GPL(trace_clock_global);

static atomic64_t trace_counter;

--
2.4.0.rc3.3.g6eb1401

2015-04-30 14:48:08

by Steven Rostedt

Subject: Re: [PATCH] tracing: Export tracing clock functions

On Thu, 30 Apr 2015 07:36:40 -0700
Jerry Snitselaar <[email protected]> wrote:

> Critical tracepoint hooks shoud never call anything that takes a lock,
> so they are unable to call getrawmonotonic() or ktime_get().
>
> Export the rest of the tracing clock functions so can be used in
> tracepoint hooks.

A little background needs to be explained here.

A customer adds their own module to do some analysis and hooks to
tracepoints to do so. They were using ktime_get() as their time source,
but as that grabs a seq lock, it was causing deadlocks.

The tracing clocks were made for this purpose, and I find nothing wrong
with letting users add their own modules (GPL of course) and adding
their own hooks to the tracepoint code. I created it for that purpose.
But if they need to do any timings, they must use lockless clocks,
which the trace clocks are good for.

-- Steve


>
> Cc: Steven Rostedt <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Signed-off-by: Jerry Snitselaar <[email protected]>
> ---

2015-04-30 15:10:28

by Jerry Snitselaar

Subject: [PATCH v2] tracing: Export tracing clock functions

Critical tracepoint hooks should never call anything that takes a lock,
so they are unable to call getrawmonotonic() or ktime_get().

Export the rest of the tracing clock functions so can be used in
tracepoint hooks.

Background: We have a customer that adds their own module and registers
a tracepoint hook to sched_wakeup. They were using ktime_get() for a
time source, but it grabs a seq lock and caused a deadlock to occur.

v2: added background info and fixed typo

Cc: Steven Rostedt <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Jerry Snitselaar <[email protected]>
---
kernel/trace/trace_clock.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index 57b67b1..0f06532 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -56,6 +56,7 @@ u64 notrace trace_clock(void)
{
return local_clock();
}
+EXPORT_SYMBOL_GPL(trace_clock);

/*
* trace_jiffy_clock(): Simply use jiffies as a clock counter.
@@ -68,6 +69,7 @@ u64 notrace trace_clock_jiffies(void)
{
return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
}
+EXPORT_SYMBOL_GPL(trace_clock_jiffies);

/*
* trace_clock_global(): special globally coherent trace clock
@@ -123,6 +125,7 @@ u64 notrace trace_clock_global(void)

return now;
}
+EXPORT_SYMBOL_GPL(trace_clock_global);

static atomic64_t trace_counter;

--
2.4.0.rc3.3.g6eb1401