linux-kernel - Re: [PATCHv3] perf tools: Add struct ordered_events

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Date:   Thu, 6 Sep 2018 15:28:59 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, mingo@...e.hu,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCHv3] perf tools: Add struct ordered_events_buffer layer

On Mon, Sep 03, 2018 at 07:37:56PM -0700, Stephane Eranian wrote:

SNIP

> 
> I think the code is correct now for the issue related to uninitialized pointer.
> But there is still one problem I found stressing the code with max_alloc_size.
> The way the following is written:
> 
>        if (!list_empty(cache)) {
>                 new = list_entry(cache->next, struct ordered_event, list);
>                 list_del(&new->list);
>         } else if (oe->buffer) {
>                 new = oe->buffer + oe->buffer_idx;
>                 if (++oe->buffer_idx == MAX_SAMPLE_BUFFER)
>                         oe->buffer = NULL;
>         } else if (oe->cur_alloc_size < oe->max_alloc_size) {
>                 size_t size = sizeof(*oe->buffer) MAX_SAMPLE_BUFFER *
> sizeof(*new);
> 
>                 oe->buffer = malloc(size);
>                 if (!oe->buffer) {
>                         free_dup_event(oe, new_event);
>                         return NULL;
>                 }
> 
>                 pr("alloc size %" PRIu64 "B (+%zu), max %" PRIu64 "B\n",
>                    oe->cur_alloc_size, size, oe->max_alloc_size);
> 
>                 oe->cur_alloc_size += size;
> 
> You can end up with oe->cur_alloc_size > oe->max_alloc_size in case
> the max limit is
> really low (< size_t size = sizeof (*oe->buffer) + MAX_SAMPLE_BUFFER *
> sizeof(*new);
> So I think to make sure you can never allocate more than the max, you
> have to do:
> 
>       size_t size = sizeof(*oe->buffer) MAX_SAMPLE_BUFFER * sizeof(*new);
>        if (!list_empty(cache)) {
>                 new = list_entry(cache->next, struct ordered_event, list);
>                 list_del(&new->list);
>         } else if (oe->buffer) {
>                 new = oe->buffer + oe->buffer_idx;
>                 if (++oe->buffer_idx == MAX_SAMPLE_BUFFER)
>                         oe->buffer = NULL;
>         } else if ((oe->cur_alloc_size + size) < oe->max_alloc_size) {
> 
> Then you will never allocate more than the max.
> I think with this change, we are okay.
> Tested-by: Stephane Eranian <eranian@...gle.com>

yep, makes sense.. something like below then
I'll post it on top of the previous patch

thanks,
jirka


---
diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
index 87171e8fd70d..2d1d0f3c8f77 100644
--- a/tools/perf/util/ordered-events.c
+++ b/tools/perf/util/ordered-events.c
@@ -101,6 +101,7 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
 	struct list_head *cache = &oe->cache;
 	struct ordered_event *new = NULL;
 	union perf_event *new_event;
+	size_t size;
 
 	new_event = dup_event(oe, event);
 	if (!new_event)
@@ -133,6 +134,8 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
 	 * Removal of ordered event object moves it from events to
 	 * the cache list.
 	 */
+	size = sizeof(*oe->buffer) + MAX_SAMPLE_BUFFER * sizeof(*new);
+
 	if (!list_empty(cache)) {
 		new = list_entry(cache->next, struct ordered_event, list);
 		list_del(&new->list);
@@ -140,10 +143,7 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
 		new = &oe->buffer->event[oe->buffer_idx];
 		if (++oe->buffer_idx == MAX_SAMPLE_BUFFER)
 			oe->buffer = NULL;
-	} else if (oe->cur_alloc_size < oe->max_alloc_size) {
-		size_t size = sizeof(*oe->buffer) +
-			      MAX_SAMPLE_BUFFER * sizeof(*new);
-
+	} else if ((oe->cur_alloc_size + size) < oe->max_alloc_size) {
 		oe->buffer = malloc(size);
 		if (!oe->buffer) {
 			free_dup_event(oe, new_event);