Re: [for-next][PATCH 05/31] tracing: Have existing event_command.parse() implementations use helpers

From: Tom Zanussi
Date: Thu Jan 13 2022 - 16:58:44 EST


Hi Steve,

On Thu, 2022-01-13 at 16:20 -0500, Steven Rostedt wrote:
> On Thu, 13 Jan 2022 18:03:07 +0100
> Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
>
> > I did some debug, and found that the histogram is working. The
> > problem is that,
> > to read the histogram I pause it to have consistent data:
> >
> > in tools/tracing/rtla/osnoise_hist.c:
> > osnoise_read_trace_hist() {
> > [...]
> > tracefs_hist_pause(tool->trace.inst, data->trace_hist);
> >
> > content = tracefs_event_file_read(tool->trace.inst,
> > "osnoise",
> > "sample_threshold",
> > "hist", NULL);
> > [...]
> > }
> >
> > and, as far as I got, after this patch, pausing the histogram makes
> > it to clear
> > up. If I comment the "tracefs_hist_pause" line, "rtla osnoise hist"
> > start
> > working back again.
> >
> > Thoughts?
>
> This is all messed up. I'm removing this patch completely.
>
> Tom, can you fix this. The issue is that it's putting too much policy
> into
> the helper functions, which is big no no.
>
> Specifically, we have:
>
> int event_trigger_register(struct event_command *cmd_ops,
> struct trace_event_file *file,
> char *glob,
> char *cmd,
> char *param,
> struct event_trigger_data *trigger_data,
> int *n_registered)
> {
> int ret;
>
> if (n_registered)
> *n_registered = 0;
>
> ret = cmd_ops->reg(glob, trigger_data, file);
> /*
> * The above returns on success the # of functions enabled,
> * but if it didn't find any functions it returns zero.
> * Consider no functions a failure too.
> */
> if (!ret) {
> cmd_ops->unreg(glob, trigger_data, file);
> ret = -ENOENT;
> } else if (ret > 0) {
> if (n_registered)
> *n_registered = ret;
> /* Just return zero, not the number of enabled
> functions */
> ret = 0;
> }
>
> return ret;
> }
>
>
> And in the case of pause, this *will* have ret = 0 on return. And
> what
> happens is that it removes the trigger completely.
>
> Look at the code in the histogram on the return:
>
> ret = event_trigger_register(cmd_ops, file, glob, cmd, param,
> trigger_data, &n_registered);
> if (ret < 0)
> goto out_free;
> if ((ret == 0) && (n_registered == 0)) {
> if (!(attrs->pause || attrs->cont || attrs->clear))
> ret = -ENOENT;
> goto out_free;
> }
>
> It checks for 0 and 0 and only errors if it's not pause, cont, or
> clear.
> Hence, all three are now broken due to this patch.
>
> I will not be adding this to this merge window.

Yes, you're right, event_trigger_register() is trying to do a little
too much, and shouldn't be doing the unreg().

Thanks for finding and figuring that out. I'll fix this and send a new
version after the merge window.

Tom

>
> -- Steve