Re: [PATCH v2 21/40] tracing: Generalize per-element hist trigger data

[Steven Rostedt]

On Tue,  5 Sep 2017 16:57:33 -0500
Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> wrote:

> Up until now, hist triggers only needed per-element support for saving
> 'comm' data, which was saved directly as a private data pointer.
> 
> In anticipation of the need to save other data besides 'comm', add a
> new hist_elt_data struct for the purpose, and switch the current
> 'comm'-related code over to that.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_hist.c | 65 ++++++++++++++++++++--------------------
>  1 file changed, 32 insertions(+), 33 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index bbca6d3..f17d394 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -249,6 +249,10 @@ static u64 hist_field_timestamp(struct hist_field *hist_field, void *event,
>  	return ts;
>  }
>  
> +struct hist_elt_data {
> +	char *comm;
> +};
> +
>  static const char *hist_field_name(struct hist_field *field,
>  				   unsigned int level)
>  {
> @@ -447,26 +451,36 @@ static inline void save_comm(char *comm, struct task_struct *task)
>  	memcpy(comm, task->comm, TASK_COMM_LEN);
>  }
>  
> -static void hist_trigger_elt_comm_free(struct tracing_map_elt *elt)
> +static void hist_trigger_elt_data_free(struct tracing_map_elt *elt)
>  {
> -	kfree((char *)elt->private_data);
> +	struct hist_elt_data *private_data = elt->private_data;

Small nit, please don't call this variable "private_data". Call it
"elt_data" like you do below. Try to keep variable names consistent.

> +
> +	kfree(private_data->comm);
> +	kfree(private_data);
>  }
>  
> -static int hist_trigger_elt_comm_alloc(struct tracing_map_elt *elt)
> +static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
>  {
>  	struct hist_trigger_data *hist_data = elt->map->private_data;
> +	unsigned int size = TASK_COMM_LEN + 1;
> +	struct hist_elt_data *elt_data;
>  	struct hist_field *key_field;
>  	unsigned int i;
>  
> +	elt->private_data = elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);

What about just allocating elt_data here, but not assigning private_data.

> +	if (!elt_data)
> +		return -ENOMEM;
> +
>  	for_each_hist_key_field(i, hist_data) {
>  		key_field = hist_data->fields[i];
>  
>  		if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
> -			unsigned int size = TASK_COMM_LEN + 1;
> -
> -			elt->private_data = kzalloc(size, GFP_KERNEL);
> -			if (!elt->private_data)
> +			elt_data->comm = kzalloc(size, GFP_KERNEL);
> +			if (!elt_data->comm) {
> +				kfree(elt_data);
> +				elt->private_data = NULL;

Then here, we don't need to remember to NULL it out.

>  				return -ENOMEM;
> +			}
>  			break;
>  		}
>  	}

Then we can have after the loop.

	elt->private_data = elt_data;


> @@ -474,18 +488,18 @@ static int hist_trigger_elt_comm_alloc(struct tracing_map_elt *elt)
>  	return 0;
>  }
>  
> -static void hist_trigger_elt_comm_init(struct tracing_map_elt *elt)
> +static void hist_trigger_elt_data_init(struct tracing_map_elt *elt)
>  {
> -	char *comm = elt->private_data;
> +	struct hist_elt_data *private_data = elt->private_data;

Again, please call this elt_data.

>  
> -	if (comm)
> -		save_comm(comm, current);
> +	if (private_data->comm)
> +		save_comm(private_data->comm, current);
>  }
>  
> -static const struct tracing_map_ops hist_trigger_elt_comm_ops = {
> -	.elt_alloc	= hist_trigger_elt_comm_alloc,
> -	.elt_free	= hist_trigger_elt_comm_free,
> -	.elt_init	= hist_trigger_elt_comm_init,
> +static const struct tracing_map_ops hist_trigger_elt_data_ops = {
> +	.elt_alloc	= hist_trigger_elt_data_alloc,
> +	.elt_free	= hist_trigger_elt_data_free,
> +	.elt_init	= hist_trigger_elt_data_init,
>  };
>  
>  static const char *get_hist_field_flags(struct hist_field *hist_field)
> @@ -1494,21 +1508,6 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
>  	return 0;
>  }
>  
> -static bool need_tracing_map_ops(struct hist_trigger_data *hist_data)
> -{
> -	struct hist_field *key_field;
> -	unsigned int i;
> -
> -	for_each_hist_key_field(i, hist_data) {
> -		key_field = hist_data->fields[i];
> -
> -		if (key_field->flags & HIST_FIELD_FL_EXECNAME)
> -			return true;
> -	}
> -
> -	return false;
> -}
> -
>  static struct hist_trigger_data *
>  create_hist_data(unsigned int map_bits,
>  		 struct hist_trigger_attrs *attrs,
> @@ -1534,8 +1533,7 @@ static bool need_tracing_map_ops(struct hist_trigger_data *hist_data)
>  	if (ret)
>  		goto free;
>  
> -	if (need_tracing_map_ops(hist_data))
> -		map_ops = &hist_trigger_elt_comm_ops;
> +	map_ops = &hist_trigger_elt_data_ops;
>  
>  	hist_data->map = tracing_map_create(map_bits, hist_data->key_size,
>  					    map_ops, hist_data);
> @@ -1724,7 +1722,8 @@ static void hist_trigger_stacktrace_print(struct seq_file *m,
>  			seq_printf(m, "%s: [%llx] %-55s", field_name,
>  				   uval, str);
>  		} else if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
> -			char *comm = elt->private_data;
> +			struct hist_elt_data *elt_data = elt->private_data;

I wonder if we should have a return WARN_ON_ONCE(!elt_data); here just
in case.

-- Steve

> +			char *comm = elt_data->comm;
>  
>  			uval = *(u64 *)(key + key_field->offset);
>  			seq_printf(m, "%s: %-16s[%10llu]",
> field_name,