linux-kernel - Re: [PATCH V3 06/15] perf tools: fix parse_events_terms() freeing local variable on error path

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Date:	Mon, 01 Jul 2013 11:01:24 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	David Ahern <dsahern@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V3 06/15] perf tools: fix parse_events_terms() freeing
 local variable on error path

On 28/06/13 20:19, David Ahern wrote:
> On 6/28/13 2:43 AM, Adrian Hunter wrote:
>> The list_head is on the stack, so just free the rest of the list.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>>   tools/perf/util/parse-events.c | 7 ++++++-
>>   tools/perf/util/parse-events.h | 1 +
>>   tools/perf/util/pmu.c          | 2 +-
>>   3 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
>> index 995fc25..d9cb055 100644
>> --- a/tools/perf/util/parse-events.c
>> +++ b/tools/perf/util/parse-events.c
>> @@ -1231,12 +1231,17 @@ int parse_events_term__clone(struct
>> parse_events_term **new,
>>               term->val.str, term->val.num);
>>   }
>>
>> -void parse_events__free_terms(struct list_head *terms)
>> +void parse_events__free_terms_only(struct list_head *terms)
>>   {
>>       struct parse_events_term *term, *h;
>>
>>       list_for_each_entry_safe(term, h, terms, list)
>>           free(term);
>> +}
>> +
>> +void parse_events__free_terms(struct list_head *terms)
>> +{
>> +    parse_events__free_terms_only(terms);
>>
>>       free(terms);
>>   }
> 
> I still don't understand the reasoning for an _only function. There is only
> 1 place that mallocs the list_head and that 1 user should free its own
> memory. All of the other users pass a stack variable.

No.  See parse-events.y

The list head is defined as a pointer in the YYTYPE stack element:

%union
{
	char *str;
	u64 num;
	struct list_head *head;
	struct parse_events_term *term;
}

It is malloc'ed when terms are created:

event_term
{
	struct list_head *head = malloc(sizeof(*head));
	struct parse_events_term *term = $1;

	ABORT_ON(!head);
	INIT_LIST_HEAD(head);
	list_add_tail(&term->list, head);
	$$ = head;
}

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