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

From: Frederic Weisbecker
Date: Tue May 19 2009 - 21:07:39 EST


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 :-)



> <= __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


Frederic.


> static void ftrace_trace_userstack(struct trace_array *tr,
> unsigned long flags, int pc)
> {
>

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