Date:	Thu, 14 Jan 2010 19:14:26 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	mingo@...e.hu
Subject: Re: [PATCH 40/40] ftrace,kdb: Extend kdb to be able to dump the
 ftrace buffer

On Thu, 2010-01-14 at 08:59 -0600, Jason Wessel wrote:
> Add in a helper function to allow the kdb shell to dump the ftrace
> buffer.
> 

Acked-by: Steven Rostedt <rostedt@...dmis.org>


If this is the final version, I could queue it up in my tree for 34, and
push it off to Ingo.

-- Steve

> Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
> ---
>  Documentation/DocBook/kgdb.tmpl |    3 +-
>  kernel/trace/Makefile           |    3 +
>  kernel/trace/trace.c            |   48 +++++++---------
>  kernel/trace/trace.h            |   17 ++++++
>  kernel/trace/trace_kdb.c        |  116 +++++++++++++++++++++++++++++++++++++++
>  5 files changed, 160 insertions(+), 27 deletions(-)
>  create mode 100644 kernel/trace/trace_kdb.c
> 
> diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl
> index bbf4a22..b01b5b1 100644
> --- a/Documentation/DocBook/kgdb.tmpl
> +++ b/Documentation/DocBook/kgdb.tmpl
> @@ -675,7 +675,8 @@ Task Addr       Pid   Parent [*] cpu State Thread     Command
>        <itemizedlist>
>          <listitem><para>A simple shell</para></listitem>
>          <listitem><para>The kdb core command set</para></listitem>
> -        <listitem><para>A registration API to register additional kdb shell commands.</para></listitem>
> +        <listitem><para>A registration API to register additional kdb shell commands.</para>
> +        <para>A good example of a self contained kdb module is the "ftdump" command for dumping the ftrace buffer.  See: kernel/trace/trace_kdb.c</para></listitem>
>          <listitem><para>The implementation for kdb_printf() which emit messages directly to I/O drivers, bypassing the kernel log.</para></listitem>
>          <listitem><para>SW / HW breakpoint management for the kdb shell</para></listitem>
>        </itemizedlist>
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index cd9ecd8..c48a28f 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -56,5 +56,8 @@ obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
>  obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
>  obj-$(CONFIG_KSYM_TRACER) += trace_ksym.o
>  obj-$(CONFIG_EVENT_TRACING) += power-traces.o
> +ifeq ($(CONFIG_TRACING),y)
> +obj-$(CONFIG_KGDB_KDB) += trace_kdb.o
> +endif
>  
>  libftrace-y := ftrace.o
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 0df1b0f..b3c786a 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -100,14 +100,11 @@ static inline void ftrace_enable_cpu(void)
>  	preempt_enable();
>  }
>  
> -static cpumask_var_t __read_mostly	tracing_buffer_mask;
> +cpumask_var_t __read_mostly	tracing_buffer_mask;
>  
>  /* Define which cpu buffers are currently read in trace_pipe */
>  static cpumask_var_t			tracing_reader_cpumask;
>  
> -#define for_each_tracing_cpu(cpu)	\
> -	for_each_cpu(cpu, tracing_buffer_mask)
> -
>  /*
>   * ftrace_dump_on_oops - variable to dump ftrace buffer on oops
>   *
> @@ -1409,11 +1406,6 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
>  }
>  EXPORT_SYMBOL_GPL(trace_vprintk);
>  
> -enum trace_file_type {
> -	TRACE_FILE_LAT_FMT	= 1,
> -	TRACE_FILE_ANNOTATE	= 2,
> -};
> -
>  static void trace_iterator_increment(struct trace_iterator *iter)
>  {
>  	/* Don't allow ftrace to trace into the ring buffers */
> @@ -1503,7 +1495,7 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
>  }
>  
>  /* Find the next real entry, and increment the iterator to the next entry */
> -static void *find_next_entry_inc(struct trace_iterator *iter)
> +void *trace_find_next_entry_inc(struct trace_iterator *iter)
>  {
>  	iter->ent = __find_next_entry(iter, &iter->cpu, &iter->ts);
>  
> @@ -1536,12 +1528,12 @@ static void *s_next(struct seq_file *m, void *v, loff_t *pos)
>  		return NULL;
>  
>  	if (iter->idx < 0)
> -		ent = find_next_entry_inc(iter);
> +		ent = trace_find_next_entry_inc(iter);
>  	else
>  		ent = iter;
>  
>  	while (ent && iter->idx < i)
> -		ent = find_next_entry_inc(iter);
> +		ent = trace_find_next_entry_inc(iter);
>  
>  	iter->pos = *pos;
>  
> @@ -1878,7 +1870,7 @@ static enum print_line_t print_bin_fmt(struct trace_iterator *iter)
>  	return event ? event->binary(iter, 0) : TRACE_TYPE_HANDLED;
>  }
>  
> -static int trace_empty(struct trace_iterator *iter)
> +int trace_empty(struct trace_iterator *iter)
>  {
>  	int cpu;
>  
> @@ -1909,7 +1901,7 @@ static int trace_empty(struct trace_iterator *iter)
>  }
>  
>  /*  Called with trace_event_read_lock() held. */
> -static enum print_line_t print_trace_line(struct trace_iterator *iter)
> +enum print_line_t print_trace_line(struct trace_iterator *iter)
>  {
>  	enum print_line_t ret;
>  
> @@ -3074,7 +3066,7 @@ waitagain:
>  	iter->pos = -1;
>  
>  	trace_event_read_lock();
> -	while (find_next_entry_inc(iter) != NULL) {
> +	while (trace_find_next_entry_inc(iter) != NULL) {
>  		enum print_line_t ret;
>  		int len = iter->seq.len;
>  
> @@ -3156,7 +3148,7 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
>  		if (ret != TRACE_TYPE_NO_CONSUME)
>  			trace_consume(iter);
>  		rem -= count;
> -		if (!find_next_entry_inc(iter))	{
> +		if (!trace_find_next_entry_inc(iter))	{
>  			rem = 0;
>  			iter->ent = NULL;
>  			break;
> @@ -3209,7 +3201,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
>  	if (ret <= 0)
>  		goto out_err;
>  
> -	if (!iter->ent && !find_next_entry_inc(iter)) {
> +	if (!iter->ent && !trace_find_next_entry_inc(iter)) {
>  		ret = -EFAULT;
>  		goto out_err;
>  	}
> @@ -4262,7 +4254,7 @@ static struct notifier_block trace_die_notifier = {
>   */
>  #define KERN_TRACE		KERN_EMERG
>  
> -static void
> +void
>  trace_printk_seq(struct trace_seq *s)
>  {
>  	/* Probably should print a warning here. */
> @@ -4277,6 +4269,13 @@ trace_printk_seq(struct trace_seq *s)
>  	trace_seq_init(s);
>  }
>  
> +void trace_init_global_iter(struct trace_iterator *iter)
> +{
> +	iter->tr = &global_trace;
> +	iter->trace = current_trace;
> +	iter->cpu_file = TRACE_PIPE_ALL_CPU;
> +}
> +
>  static void __ftrace_dump(bool disable_tracing)
>  {
>  	static arch_spinlock_t ftrace_dump_lock =
> @@ -4301,8 +4300,10 @@ static void __ftrace_dump(bool disable_tracing)
>  	if (disable_tracing)
>  		ftrace_kill();
>  
> +	trace_init_global_iter(&iter);
> +
>  	for_each_tracing_cpu(cpu) {
> -		atomic_inc(&global_trace.data[cpu]->disabled);
> +		atomic_inc(&iter.tr->data[cpu]->disabled);
>  	}
>  
>  	old_userobj = trace_flags & TRACE_ITER_SYM_USEROBJ;
> @@ -4312,11 +4313,6 @@ static void __ftrace_dump(bool disable_tracing)
>  
>  	printk(KERN_TRACE "Dumping ftrace buffer:\n");
>  
> -	/* Simulate the iterator */
> -	iter.tr = &global_trace;
> -	iter.trace = current_trace;
> -	iter.cpu_file = TRACE_PIPE_ALL_CPU;
> -
>  	/*
>  	 * We need to stop all tracing on all CPUS to read the
>  	 * the next buffer. This is a bit expensive, but is
> @@ -4338,7 +4334,7 @@ static void __ftrace_dump(bool disable_tracing)
>  		iter.iter_flags |= TRACE_FILE_LAT_FMT;
>  		iter.pos = -1;
>  
> -		if (find_next_entry_inc(&iter) != NULL) {
> +		if (trace_find_next_entry_inc(&iter) != NULL) {
>  			int ret;
>  
>  			ret = print_trace_line(&iter);
> @@ -4359,7 +4355,7 @@ static void __ftrace_dump(bool disable_tracing)
>  		trace_flags |= old_userobj;
>  
>  		for_each_tracing_cpu(cpu) {
> -			atomic_dec(&global_trace.data[cpu]->disabled);
> +			atomic_dec(&iter.tr->data[cpu]->disabled);
>  		}
>  		tracing_on();
>  	}
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 4df6a77..563e6f8 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -352,6 +352,12 @@ struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
>  struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
>  					  int *ent_cpu, u64 *ent_ts);
>  
> +int trace_empty(struct trace_iterator *iter);
> +
> +void *trace_find_next_entry_inc(struct trace_iterator *iter);
> +
> +void trace_init_global_iter(struct trace_iterator *iter);
> +
>  void default_wait_pipe(struct trace_iterator *iter);
>  void poll_wait_pipe(struct trace_iterator *iter);
>  
> @@ -391,6 +397,15 @@ void tracing_start_sched_switch_record(void);
>  int register_tracer(struct tracer *type);
>  void unregister_tracer(struct tracer *type);
>  int is_tracing_stopped(void);
> +enum trace_file_type {
> +	TRACE_FILE_LAT_FMT	= 1,
> +	TRACE_FILE_ANNOTATE	= 2,
> +};
> +
> +extern cpumask_var_t __read_mostly tracing_buffer_mask;
> +
> +#define for_each_tracing_cpu(cpu)	\
> +	for_each_cpu(cpu, tracing_buffer_mask)
>  
>  extern int process_new_ksym_entry(char *ksymname, int op, unsigned long addr);
>  
> @@ -483,6 +498,8 @@ trace_array_vprintk(struct trace_array *tr,
>  		    unsigned long ip, const char *fmt, va_list args);
>  int trace_array_printk(struct trace_array *tr,
>  		       unsigned long ip, const char *fmt, ...);
> +void trace_printk_seq(struct trace_seq *s);
> +enum print_line_t print_trace_line(struct trace_iterator *iter);
>  
>  extern unsigned long trace_flags;
>  
> diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
> new file mode 100644
> index 0000000..9227ff3
> --- /dev/null
> +++ b/kernel/trace/trace_kdb.c
> @@ -0,0 +1,116 @@
> +/*
> + * kdb helper for dumping the ftrace buffer
> + *
> + * Copyright (C) 2010 Jason Wessel <jason.wessel@...driver.com>
> + *
> + * ftrace_dump_buf based on ftrace_dump:
> + * Copyright (C) 2007-2008 Steven Rostedt <srostedt@...hat.com>
> + * Copyright (C) 2008 Ingo Molnar <mingo@...hat.com>
> + *
> + */
> +#include <linux/init.h>
> +#include <linux/kgdb.h>
> +#include <linux/kdb.h>
> +#include <linux/ftrace.h>
> +
> +#include "../debug/kdb/kdb_private.h"
> +#include "trace.h"
> +#include "trace_output.h"
> +
> +static void ftrace_dump_buf(int skip_lines)
> +{
> +	/* use static because iter can be a bit big for the stack */
> +	static struct trace_iterator iter;
> +	unsigned int old_userobj;
> +	int cnt = 0, cpu;
> +
> +	trace_init_global_iter(&iter);
> +
> +	for_each_tracing_cpu(cpu) {
> +		atomic_inc(&iter.tr->data[cpu]->disabled);
> +	}
> +
> +	old_userobj = trace_flags;
> +
> +	/* don't look at user memory in panic mode */
> +	trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
> +
> +	kdb_printf("Dumping ftrace buffer:\n");
> +
> +	/* reset all but tr, trace, and overruns */
> +	memset(&iter.seq, 0,
> +		   sizeof(struct trace_iterator) -
> +		   offsetof(struct trace_iterator, seq));
> +	iter.iter_flags |= TRACE_FILE_LAT_FMT;
> +	iter.pos = -1;
> +
> +	for_each_tracing_cpu(cpu)
> +		iter.buffer_iter[cpu] =
> +			ring_buffer_read_start(iter.tr->buffer, cpu);
> +
> +	if (!trace_empty(&iter))
> +		trace_find_next_entry_inc(&iter);
> +	while (!trace_empty(&iter)) {
> +		if (!cnt)
> +			kdb_printf("---------------------------------\n");
> +		cnt++;
> +
> +		if (trace_find_next_entry_inc(&iter) != NULL && !skip_lines)
> +			print_trace_line(&iter);
> +		if (!skip_lines)
> +			trace_printk_seq(&iter.seq);
> +		else
> +			skip_lines--;
> +		if (KDB_FLAG(CMD_INTERRUPT))
> +			goto out;
> +	}
> +
> +	if (!cnt)
> +		kdb_printf("   (ftrace buffer empty)\n");
> +	else
> +		kdb_printf("---------------------------------\n");
> +
> +out:
> +	trace_flags = old_userobj;
> +
> +	for_each_tracing_cpu(cpu) {
> +		atomic_dec(&iter.tr->data[cpu]->disabled);
> +	}
> +
> +	for_each_tracing_cpu(cpu)
> +		if (iter.buffer_iter[cpu])
> +			ring_buffer_read_finish(iter.buffer_iter[cpu]);
> +}
> +
> +/*
> + * kdb_ftdump - Dump the ftrace log buffer
> + */
> +static int kdb_ftdump(int argc, const char **argv)
> +{
> +	int skip_lines = 0;
> +	char *cp;
> +
> +	if (argc > 1)
> +		return KDB_ARGCOUNT;
> +
> +	if (argc) {
> +		skip_lines = simple_strtol(argv[1], &cp, 0);
> +		if (*cp)
> +			skip_lines = 0;
> +	}
> +
> +	kdb_trap_printk++;
> +	ftrace_dump_buf(skip_lines);
> +	kdb_trap_printk--;
> +
> +	return 0;
> +}
> +
> +static __init int kdb_ftrace_register(void)
> +{
> +	kdb_register_repeat("ftdump", kdb_ftdump, "", "Dump ftrace log",
> +			    0, KDB_REPEAT_NONE);
> +	return 0;
> +}
> +
> +late_initcall(kdb_ftrace_register);


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