On 06/18, Steven Rostedt wrote:
>
> On Tue, 2013-06-18 at 21:22 +0200, Oleg Nesterov wrote:
> > @@ -663,6 +663,12 @@ perf_trace_##call(void *__data, proto)
> > \
> > int rctx; \
> > \
> > __data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
> > + \
> > + head = this_cpu_ptr(event_call->perf_events); \
> > + if (__builtin_constant_p(!__task) && !__task && \
>
>
> I'm trying to wrap my head around this:
>
> __builtin_constant_p(!task)
>
> is this the same as:
>
> !__builtin_constant_p(task)
>
> Or is it the same as:
>
> __builtin_constant_p(task)
>
> ?
>
> Because that '!' is confusing the heck out of me.
>
> If !task is a constant, wouldn't task be a constant too, and if task is
> not a constant then I would also assume !task is not a constant as well.
!__task looks more explicit/symmetrical to me. We need
if (is_compile_time_true(!__task)) && list_empty)
return;
is_compile_time_true(cond) could be defined as
__builtin_constant_p(cond) && (cond)
or
__builtin_constant_p(!cond) && (cond)
but the 1ts one looks more clean.
However,
> If this is the case, can we nuke the '!' from the builtin_consant_p().
OK, I do not really mind, will do.
And,
> Or is this your way to confuse me as much as my code has confused
> you? ;-)
Of course! this was the main reason.
Steven, I convinced myself the patch should be correct. If you agree with
this hack:
- anything else I should do apart from the change above?
- should I resend the previous "[PATCH 0/3] tracing: more
list_empty(perf_events) checks" series?
This series depends on "[PATCH 3/3] tracing/perf: Move the
PERF_MAX_TRACE_SIZE check into perf_trace_buf_prepare()".
Or I can drop this patch if you do not like it and rediff.
Just in case, there are other pending patches in trace_kprobe.c
which I am going to resend, but they are orthogonal.
Oleg.
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