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SubjectRe: [PATCH v2 21/40] tracing: Generalize per-element hist trigger data
On Tue,  5 Sep 2017 16:57:33 -0500
Tom Zanussi <tom.zanussi@linux.intel.com> 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@linux.intel.com>
> ---
> 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,

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