Re: [PATCH 4/7] uprobes/perf: Teach trace_uprobe/perf code to track the active perf_event's

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2013-02-04 20:02:54]:

> Introduce "struct trace_uprobe_filter" which records the "active"
> perf_event's attached to ftrace_event_call. For the start we simply
> use list_head, we can optimize this later if needed. For example, we
> do not really need to record an event with ->parent != NULL, we can
> rely on parent->child_list. And we can certainly do some optimizations
> for the case when 2 events have the same ->tp_target or tp_target->mm.
> 
> Change trace_uprobe_register() to process TRACE_REG_PERF_OPEN/CLOSE
> and add/del this perf_event to the list.
> 
> We can probably avoid any locking, but lets start with the "obvioulsy
> correct" trace_uprobe_filter->rwlock which protects everything.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>


Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  kernel/trace/trace_uprobe.c |   55 +++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 55 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 0a9a8de..f05ec32 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -28,6 +28,12 @@
> 
>  #define UPROBE_EVENT_SYSTEM	"uprobes"
> 
> +struct trace_uprobe_filter {
> +	rwlock_t		rwlock;
> +	int			nr_systemwide;
> +	struct list_head	perf_events;
> +};
> +
>  /*
>   * uprobe event core functions
>   */
> @@ -35,6 +41,7 @@ struct trace_uprobe {
>  	struct list_head		list;
>  	struct ftrace_event_class	class;
>  	struct ftrace_event_call	call;
> +	struct trace_uprobe_filter	filter;
>  	struct uprobe_consumer		consumer;
>  	struct inode			*inode;
>  	char				*filename;
> @@ -58,6 +65,18 @@ static LIST_HEAD(uprobe_list);
> 
>  static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs);
> 
> +static inline void init_trace_uprobe_filter(struct trace_uprobe_filter *filter)
> +{
> +	rwlock_init(&filter->rwlock);
> +	filter->nr_systemwide = 0;
> +	INIT_LIST_HEAD(&filter->perf_events);
> +}
> +
> +static inline bool uprobe_filter_is_empty(struct trace_uprobe_filter *filter)
> +{
> +	return !filter->nr_systemwide && list_empty(&filter->perf_events);
> +}
> +
>  /*
>   * Allocate new trace_uprobe and initialize it (including uprobes).
>   */
> @@ -87,6 +106,7 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs)
> 
>  	INIT_LIST_HEAD(&tu->list);
>  	tu->consumer.handler = uprobe_dispatcher;
> +	init_trace_uprobe_filter(&tu->filter);
>  	return tu;
> 
>  error:
> @@ -541,6 +561,8 @@ static int probe_event_enable(struct trace_uprobe *tu, int flag)
>  	if (is_trace_uprobe_enabled(tu))
>  		return -EINTR;
> 
> +	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> +
>  	tu->flags |= flag;
>  	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>  	if (ret)
> @@ -554,6 +576,8 @@ static void probe_event_disable(struct trace_uprobe *tu, int flag)
>  	if (!is_trace_uprobe_enabled(tu))
>  		return;
> 
> +	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> +
>  	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>  	tu->flags &= ~flag;
>  }
> @@ -629,6 +653,30 @@ static int set_print_fmt(struct trace_uprobe *tu)
>  }
> 
>  #ifdef CONFIG_PERF_EVENTS
> +static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
> +{
> +	write_lock(&tu->filter.rwlock);
> +	if (event->hw.tp_target)
> +		list_add(&event->hw.tp_list, &tu->filter.perf_events);
> +	else
> +		tu->filter.nr_systemwide++;
> +	write_unlock(&tu->filter.rwlock);
> +
> +	return 0;
> +}
> +
> +static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
> +{
> +	write_lock(&tu->filter.rwlock);
> +	if (event->hw.tp_target)
> +		list_del(&event->hw.tp_list);
> +	else
> +		tu->filter.nr_systemwide--;
> +	write_unlock(&tu->filter.rwlock);
> +
> +	return 0;
> +}
> +
>  /* uprobe profile handler */
>  static void uprobe_perf_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  {
> @@ -684,6 +732,13 @@ int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type,
>  	case TRACE_REG_PERF_UNREGISTER:
>  		probe_event_disable(tu, TP_FLAG_PROFILE);
>  		return 0;
> +
> +	case TRACE_REG_PERF_OPEN:
> +		return uprobe_perf_open(tu, data);
> +
> +	case TRACE_REG_PERF_CLOSE:
> +		return uprobe_perf_close(tu, data);
> +
>  #endif
>  	default:
>  		return 0;
> -- 
> 1.5.5.1
> 

-- 
Thanks and Regards
Srikar Dronamraju