Re: [PATCH][GIT PULL] tracing: add trace_stack interface

From: Steven Rostedt
Date: Tue May 19 2009 - 21:14:32 EST



On Wed, 20 May 2009, Frederic Weisbecker wrote:

> On Tue, May 19, 2009 at 08:44:50PM -0400, Steven Rostedt wrote:
> >
> > Ingo,
> >
> > Please pull the latest tip/tracing/ftrace tree, which can be found at:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> > tip/tracing/ftrace
> >
> >
> > Steven Rostedt (1):
> > tracing: add trace_stack interface
> >
> > ----
> > include/linux/kernel.h | 2 ++
> > kernel/trace/trace.c | 15 +++++++++++++++
> > 2 files changed, 17 insertions(+), 0 deletions(-)
> > ---------------------------
> > commit b85d1029ba534376d203c3ac83a2e5a4d6876cb6
> > Author: Steven Rostedt <srostedt@xxxxxxxxxx>
> > Date: Tue May 19 18:54:16 2009 -0400
> >
> > tracing: add trace_stack interface
> >
> > This patch adds the global function
> >
> > void trace_stack(void)
> >
> > This allows a developer to find where a function is called. For example,
> > if you want to know who calls __netif_reschedule, you can add
> >
> > static inline void __netif_reschedule(struct Qdisc *q)
> > {
> > struct softnet_data *sd;
> > unsigned long flags;
> >
> > + trace_stack();
> > local_irq_save(flags);
> > sd = &__get_cpu_var(softnet_data);
> > q->next_sched = sd->output_queue;
> >
> > And see the following in the trace output:
> >
> > <= __ftrace_trace_stack
> > <= trace_stack
>
>
>
> I guess the depth should begin here :-)

Yeah, I thought about that but since it only prints out the stack trace,
this is sorta the "this is a stack trace" header.
>
>
>
> > <= __netif_schedule
> > <= dev_watchdog
> > <= run_timer_softirq
> > <= __do_softirq
> > <= call_softirq
> > <= do_softirq
> > <= irq_exit
> >
> > Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> >
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index 883cd44..347a0f1 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -511,6 +511,7 @@ extern int
> > __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap);
> >
> > extern void ftrace_dump(void);
> > +extern void trace_stack(void);
> > #else
> > static inline void
> > ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3) { }
> > @@ -531,6 +532,7 @@ ftrace_vprintk(const char *fmt, va_list ap)
> > return 0;
> > }
> > static inline void ftrace_dump(void) { }
> > +static inline void trace_stack(void) { }
> > #endif /* CONFIG_TRACING */
> >
> > /*
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index dd40d23..33ab502 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -1046,6 +1046,21 @@ void __trace_stack(struct trace_array *tr,
> > __ftrace_trace_stack(tr, flags, skip, pc);
> > }
> >
> > +/**
> > + * trace_stack - dump the stack into the trace buffer
> > + *
> > + * Use this to record the stack trace into the ring buffer. If you
> > + * want to know a caller of a function, place a call to trace_stack
> > + * and the ftrace trace file will display who the callers were.
> > + */
> > +void trace_stack(void)
> > +{
> > + unsigned long flags;
> > +
> > + local_save_flags(flags);
> > + __trace_stack(&global_trace, flags, 0, preempt_count());
> > +}
>
>
>
> Stupidly I use a very similar patch while working on reiserfs
> but I forgot to post it.
>
> Another trick is to use trace_printk() combined with:
>
> echo stacktrace > trace_option

Yeah, but when you are debugging development work, doing that at every
boot up becomes a pain. You can add it to a rc script but still.

I wrote this because of the development I'm doing in the interrupt
threads. I was using this a lot to find what is calling what.

-- Steve

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