Peter Zijlstra <pet...@infradead.org> writes:
> On Fri, Dec 11, 2015 at 04:28:54PM +0100, Peter Zijlstra wrote:
>> On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
>>
>> > @@ -9063,6 +9621,18 @@ inherit_event(struct perf_event *parent_event,
>> > get_ctx(child_ctx);
>> >
>> > /*
>> > + * Clone itrace filters from the parent, if any
>> > + */
>> > + if (has_itrace_filter(child_event)) {
>> > + if (perf_itrace_filters_clone(child_event, parent_event,
>> > + child)) {
>> > + put_ctx(child_ctx);
>> > + free_event(child_event);
>> > + return NULL;
>>
>> So inherit_event()'s return policy is somewhat opaque, there's 3
>> possible returns:
>>
>> 1) a valid struct perf_event pointer; the clone was successful
>> 2) ERR_PTR(err), the clone failed, abort inherit_group, fail fork()
>> 3) NULL, the clone failed, ignore, continue
>>
>> We return NULL under two special cases:
>>
>> - the original event doesn't exist anymore, we're an orphan, do not make
>> more orphans.
>>
>> - the parent event is dying
>>
>>
>> I'm fairly sure this return should be in the 2) category. If we cannot
>> fully clone the event something bad happened, we should not ignore it.
>
> On second thought; we should not inherit the filters at all.
>
> We should always use event->parent (if exists) for filters. Otherwise
> inherited events will get different filters if you change the filter
> after clone.
But children will have different mappings, so the actual filter
configurations will still differ between parents and children. I guess I
could split the filter in two parts: one that's defined by the user and
one that we calculated from vma addresses, that we later program into
hardware.
Regards,
--
Alex
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