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

* 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.

>
> Acked-by: Frederic Weisbecker <fweisbec@gmail.com>

thanks - i also queued up a fix for the kfree() bug.

Ingo


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