Re: [PATCH 1/4] tracing: add run-time field descriptions for event filtering

[Frederic Weisbecker <fweisbec@gmail.com>]

On Sun, Mar 22, 2009 at 06:44:43PM +0100, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@gmail.com> wrote:
> 
> > Hi Tom,
> > 
> > 
> > On Sun, Mar 22, 2009 at 03:30:39AM -0500, Tom Zanussi wrote:
> > > This patch makes the field descriptions defined for event tracing
> > > available at run-time, for the event-filtering mechanism introduced in a
> > > subsequent patch.
> > > 
> > > The common event fields are prepended with 'common_' in the format
> > > display, allowing them to be distinguished from the other fields that
> > > might internally have same name and can therefore be unambiguously used
> > > in filters.
> > > 
> > > Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
> > > 
> > > ---
> > >  kernel/trace/trace.h                |   30 ++++++++++++++++-------
> > >  kernel/trace/trace_events.c         |   40 ++++++++++++++++++++++++++++++-
> > >  kernel/trace/trace_events_stage_2.h |   45 +++++++++++++++++++++++++++++++++++
> > >  kernel/trace/trace_events_stage_3.h |    2 +
> > >  4 files changed, 107 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > > index 7cfb741..9288dc7 100644
> > > --- a/kernel/trace/trace.h
> > > +++ b/kernel/trace/trace.h
> > > @@ -775,16 +775,26 @@ enum {
> > >  	TRACE_EVENT_TYPE_RAW		= 2,
> > >  };
> > >  
> > > +struct ftrace_event_field {
> > > +	struct list_head	link;
> > > +	char			*name;
> > > +	char			*type;
> > > +	int			offset;
> > > +	int			size;
> > > +};
> > > +
> > >  struct ftrace_event_call {
> > > -	char		*name;
> > > -	char		*system;
> > > -	struct dentry	*dir;
> > > -	int		enabled;
> > > -	int		(*regfunc)(void);
> > > -	void		(*unregfunc)(void);
> > > -	int		id;
> > > -	int		(*raw_init)(void);
> > > -	int		(*show_format)(struct trace_seq *s);
> > > +	char			*name;
> > > +	char			*system;
> > > +	struct dentry		*dir;
> > > +	int			enabled;
> > > +	int			(*regfunc)(void);
> > > +	void			(*unregfunc)(void);
> > > +	int			id;
> > > +	int			(*raw_init)(void);
> > > +	int			(*show_format)(struct trace_seq *s);
> > > +	int			(*define_fields)(void);
> > > +	struct list_head	fields;
> > >  
> > >  #ifdef CONFIG_EVENT_PROFILE
> > >  	atomic_t	profile_count;
> > > @@ -793,6 +803,8 @@ struct ftrace_event_call {
> > >  #endif
> > >  };
> > >  
> > > +int trace_define_field(struct ftrace_event_call *call, char *type,
> > > +		       char *name, int offset, int size);
> > >  void event_trace_printk(unsigned long ip, const char *fmt, ...);
> > >  extern struct ftrace_event_call __start_ftrace_events[];
> > >  extern struct ftrace_event_call __stop_ftrace_events[];
> > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> > > index 3047b56..961b057 100644
> > > --- a/kernel/trace/trace_events.c
> > > +++ b/kernel/trace/trace_events.c
> > > @@ -19,6 +19,34 @@
> > >  
> > >  static DEFINE_MUTEX(event_mutex);
> > >  
> > > +int trace_define_field(struct ftrace_event_call *call, char *type,
> > > +		       char *name, int offset, int size)
> > > +{
> > > +	struct ftrace_event_field *field;
> > > +
> > > +	field = kmalloc(sizeof(*field), GFP_KERNEL);
> > > +	if (!field)
> > > +		goto err;
> > > +	field->name = kstrdup(name, GFP_KERNEL);
> > > +	if (!field->name)
> > > +		goto err;
> > > +	field->type = kstrdup(type, GFP_KERNEL);
> > > +	if (!field->type)
> > > +		goto err;
> > > +	field->offset = offset;
> > > +	field->size = size;
> > > +	list_add(&field->link, &call->fields);
> > > +
> > > +	return 0;
> > > +err:
> > > +	if (field) {
> > > +		kfree(field->name);
> > > +		kfree(field->type);
> > 
> > 
> > You need kzalloc to allocate field.
> > With kmalloc, field will point to random filled memory
> > after a fresh allocation.
> > 
> > Imagine this path:
> > 
> > if (!field->name)
> > 	goto err;
> > ...
> > err:
> > 	kfree(field->name) <- field->name = NULL, correct
> > 	kfree(field->type) <- field->type = ?
> > 
> > 
> > > +	}
> > > +	kfree(field);
> > > +	return -ENOMEM;
> > > +}
> > > +
> > >  static void ftrace_clear_events(void)
> > >  {
> > >  	struct ftrace_event_call *call = (void *)__start_ftrace_events;
> > > @@ -343,7 +371,8 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
> > >  
> > >  #undef FIELD
> > >  #define FIELD(type, name)						\
> > > -	#type, #name, offsetof(typeof(field), name), sizeof(field.name)
> > > +	#type, "common_" #name, offsetof(typeof(field), name),		\
> > > +		sizeof(field.name)
> > >  
> > >  static int trace_write_header(struct trace_seq *s)
> > >  {
> > > @@ -581,6 +610,15 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
> > >  					call->name);
> > >  	}
> > >  
> > > +	if (call->define_fields) {
> > > +		ret = call->define_fields();
> > > +		if (ret < 0) {
> > > +			pr_warning("Could not initialize trace point"
> > > +				   " events/%s\n", call->name);
> > > +			return ret;
> > > +		}
> > > +	}
> > > +
> > >  	/* A trace may not want to export its format */
> > >  	if (!call->show_format)
> > >  		return 0;
> > > diff --git a/kernel/trace/trace_events_stage_2.h b/kernel/trace/trace_events_stage_2.h
> > > index 5117c43..30743f7 100644
> > > --- a/kernel/trace/trace_events_stage_2.h
> > > +++ b/kernel/trace/trace_events_stage_2.h
> > > @@ -129,3 +129,48 @@ ftrace_format_##call(struct trace_seq *s)				\
> > >  }
> > >  
> > >  #include <trace/trace_event_types.h>
> > > +
> > > +#undef __field
> > > +#define __field(type, item)						\
> > > +	ret = trace_define_field(event_call, #type, #item,		\
> > > +				 offsetof(typeof(field), item),		\
> > > +				 sizeof(field.item));			\
> > > +	if (ret)							\
> > > +		return ret;
> > > +
> > > +#undef __array
> > > +#define __array(type, item, len)					\
> > > +	ret = trace_define_field(event_call, #type "[" #len "]", #item,	\
> > > +				 offsetof(typeof(field), item),		\
> > > +				 sizeof(field.item));			\
> > > +	if (ret)							\
> > > +		return ret;
> > > +
> > > +#define __common_field(type, item)					\
> > > +	ret = trace_define_field(event_call, #type, "common_" #item,	\
> > > +				 offsetof(typeof(field.ent), item),	\
> > > +				 sizeof(field.ent.item));		\
> > > +	if (ret)							\
> > > +		return ret;
> > > +
> > > +#undef TRACE_EVENT
> > > +#define TRACE_EVENT(call, proto, args, tstruct, func, print)		\
> > > +int									\
> > > +ftrace_define_fields_##call(void)					\
> > > +{									\
> > > +	struct ftrace_raw_##call field;					\
> > > +	struct ftrace_event_call *event_call = &event_##call;		\
> > > +	int ret;							\
> > > +									\
> > > +	__common_field(unsigned char, type);				\
> > > +	__common_field(unsigned char, flags);				\
> > > +	__common_field(unsigned char, preempt_count);			\
> > > +	__common_field(int, pid);					\
> > > +	__common_field(int, tgid);					\
> > > +									\
> > > +	tstruct;							\
> > > +									\
> > > +	return ret;							\
> > > +}
> > > +
> > > +#include <trace/trace_event_types.h>
> > > diff --git a/kernel/trace/trace_events_stage_3.h b/kernel/trace/trace_events_stage_3.h
> > > index 6b3261c..468938f 100644
> > > --- a/kernel/trace/trace_events_stage_3.h
> > > +++ b/kernel/trace/trace_events_stage_3.h
> > > @@ -252,6 +252,7 @@ static int ftrace_raw_init_event_##call(void)				\
> > >  	if (!id)							\
> > >  		return -ENODEV;						\
> > >  	event_##call.id = id;						\
> > > +	INIT_LIST_HEAD(&event_##call.fields);				\
> > >  	return 0;							\
> > >  }									\
> > >  									\
> > > @@ -264,6 +265,7 @@ __attribute__((section("_ftrace_events"))) event_##call = {		\
> > >  	.regfunc		= ftrace_raw_reg_event_##call,		\
> > >  	.unregfunc		= ftrace_raw_unreg_event_##call,	\
> > >  	.show_format		= ftrace_format_##call,			\
> > > +	.define_fields		= ftrace_define_fields_##call,		\
> > >  	_TRACE_PROFILE_INIT(call)					\
> > >  }
> > >  
> >  
> > Other than the small possible memory leak, it looks good.
> 
> it's not a memory leak but an incorrect kfree(), which can crash the 
> box.


Yeah, indeed.

 
> > 
> > Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
> 
> thanks - i also queued up a fix for the kfree() bug.
> 
> 	Ingo


Thanks.