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Subject[PATCH] perf tools: Add struct ordered_events_buffer layer
On Fri, Aug 10, 2018 at 01:54:31PM +0200, Jiri Olsa wrote:
> On Fri, Aug 10, 2018 at 01:21:18AM -0700, Stephane Eranian wrote:
> > On Thu, Aug 9, 2018 at 1:07 AM Jiri Olsa <jolsa@redhat.com> wrote:
> > >
> > > On Wed, Aug 08, 2018 at 03:33:20PM -0700, Stephane Eranian wrote:
> > > > This patch fixes a bug in ordered_event.c:alloc_event().
> > > > An ordered_event struct was not initialized properly potentially
> > > > causing crashes later on in free_dup_event() depending on the
> > > > content of the memory. If it was NULL, then it would work fine,
> > > > otherwise, it could cause crashes such as:
> > >
> > > I'm now little puzzled what do we use this first event for..
> > > I can't see anything special about it, other than it's added
> > > on the list uninitialized ;-)
> > >
> > > it seems to work properly when we ditch it.. might be some
> > > prehistoric leftover or I'm terribly missing something
> > >
> > You need to keep track of the buffers to free. You do not free the
> > ordered_event structs
> > individually. For each oe->buffer, you need one free(). Each buffer is
> > put in the to_free
> > list. But to link it into the list it needs a list_head. This is what
> > buffer[0] is used for.
> > But the logic is broken in ordered_events__free(). It does not free individual
> > ordered_event structs, but a buffer with many. Yet, it is missing
> > freeing all of the duped
> > events.
> >
> > void ordered_events__free(struct ordered_events *oe)
> > {
> > while (!list_empty(&oe->to_free)) {
> > struct ordered_event *buffer;
> >
> > buffer = list_entry(oe->to_free.next, struct
> > ordered_event, list);
> > list_del(&buffer->list);
> > ----> free_dup_event(oe, event->event);
> > free(buffer);
> > }
> > }
> > This only frees the dup_event of buffer[0] which we know is NULL (well, now).
> > It needs to walk all the entries in buffer[] to free buffer[x].event.
>
> yes.. if there's copy_on_queue set, we need to do that,
> otherwise we're leaking all the events
>
> >
> > I think the goal was likely to avoid adding another list_head field to
> > each ordered_event
> > and instead use one per allocated buffer.
> > This is very convoluted and prone to errors and we are seeing right
> > now. This should
> > be cleaned. So either you add a list_head to ordered_event or you
> > would buffer[x] in
> > ordered_events_free().
> >
> > At this point, this is my understanding.
> > Do you agree?
>
> yea, I see it now.. thanks for pointing this out
>
> how about something like below? haven't tested properly yet

attaching full patch

thanks,
jirka


---
When ordering events, we use preallocated buffers to store separated
events. Those buffers currently don't have their own struct, but since
they are basically array of 'struct ordered_event' objects, we use the
first event to hold buffers data - list head, that holds all buffers
together:

struct ordered_events {
...
struct ordered_event *buffer;
...
};

struct ordered_event {
u64 timestamp;
u64 file_offset;
union perf_event *event;
struct list_head list;
};

This is quite convoluted and error prone as demonstrated by
free-ing issue discovered and fixed by Stephane in here [1].

This patch adds the 'struct ordered_events_buffer' object,
that holds the buffer data and frees it up properly.

[1] - https://marc.info/?l=linux-kernel&m=153376761329335&w=2

Reported-by: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-qrkcqm5m1sugy4q83pfn5a1r@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/perf/util/ordered-events.c | 44 ++++++++++++++++++++++----------
tools/perf/util/ordered-events.h | 37 +++++++++++++++------------
2 files changed, 52 insertions(+), 29 deletions(-)

diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
index bad9e0296e9a..038515a52e2c 100644
--- a/tools/perf/util/ordered-events.c
+++ b/tools/perf/util/ordered-events.c
@@ -80,14 +80,20 @@ static union perf_event *dup_event(struct ordered_events *oe,
return oe->copy_on_queue ? __dup_event(oe, event) : event;
}

-static void free_dup_event(struct ordered_events *oe, union perf_event *event)
+static void __free_dup_event(struct ordered_events *oe, union perf_event *event)
{
- if (event && oe->copy_on_queue) {
+ if (event) {
oe->cur_alloc_size -= event->header.size;
free(event);
}
}

+static void free_dup_event(struct ordered_events *oe, union perf_event *event)
+{
+ if (oe->copy_on_queue)
+ __free_dup_event(oe, event);
+}
+
#define MAX_SAMPLE_BUFFER (64 * 1024 / sizeof(struct ordered_event))
static struct ordered_event *alloc_event(struct ordered_events *oe,
union perf_event *event)
@@ -104,11 +110,12 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
new = list_entry(cache->next, struct ordered_event, list);
list_del(&new->list);
} else if (oe->buffer) {
- new = oe->buffer + oe->buffer_idx;
+ 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 = MAX_SAMPLE_BUFFER * sizeof(*new);
+ size_t size = sizeof(*oe->buffer) +
+ MAX_SAMPLE_BUFFER * sizeof(*new);

oe->buffer = malloc(size);
if (!oe->buffer) {
@@ -122,9 +129,8 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
oe->cur_alloc_size += size;
list_add(&oe->buffer->list, &oe->to_free);

- /* First entry is abused to maintain the to_free list. */
- oe->buffer_idx = 2;
- new = oe->buffer + 1;
+ oe->buffer_idx = 1;
+ new = &oe->buffer->event[0];
} else {
pr("allocation limit reached %" PRIu64 "B\n", oe->max_alloc_size);
}
@@ -300,15 +306,27 @@ void ordered_events__init(struct ordered_events *oe, ordered_events__deliver_t d
oe->deliver = deliver;
}

+static void
+ordered_events_buffer__free(struct ordered_events_buffer *buffer,
+ struct ordered_events *oe)
+{
+ if (oe->copy_on_queue) {
+ unsigned int i;
+
+ for (i = 0; i < MAX_SAMPLE_BUFFER; i++)
+ __free_dup_event(oe, buffer->event[i].event);
+ }
+
+ free(buffer);
+}
+
void ordered_events__free(struct ordered_events *oe)
{
- while (!list_empty(&oe->to_free)) {
- struct ordered_event *event;
+ struct ordered_events_buffer *buffer, *tmp;

- event = list_entry(oe->to_free.next, struct ordered_event, list);
- list_del(&event->list);
- free_dup_event(oe, event->event);
- free(event);
+ list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {
+ list_del(&buffer->list);
+ ordered_events_buffer__free(buffer, oe);
}
}

diff --git a/tools/perf/util/ordered-events.h b/tools/perf/util/ordered-events.h
index 8c7a2948593e..1338d5c345dc 100644
--- a/tools/perf/util/ordered-events.h
+++ b/tools/perf/util/ordered-events.h
@@ -25,23 +25,28 @@ struct ordered_events;
typedef int (*ordered_events__deliver_t)(struct ordered_events *oe,
struct ordered_event *event);

+struct ordered_events_buffer {
+ struct list_head list;
+ struct ordered_event event[0];
+};
+
struct ordered_events {
- u64 last_flush;
- u64 next_flush;
- u64 max_timestamp;
- u64 max_alloc_size;
- u64 cur_alloc_size;
- struct list_head events;
- struct list_head cache;
- struct list_head to_free;
- struct ordered_event *buffer;
- struct ordered_event *last;
- ordered_events__deliver_t deliver;
- int buffer_idx;
- unsigned int nr_events;
- enum oe_flush last_flush_type;
- u32 nr_unordered_events;
- bool copy_on_queue;
+ u64 last_flush;
+ u64 next_flush;
+ u64 max_timestamp;
+ u64 max_alloc_size;
+ u64 cur_alloc_size;
+ struct list_head events;
+ struct list_head cache;
+ struct list_head to_free;
+ struct ordered_events_buffer *buffer;
+ struct ordered_event *last;
+ ordered_events__deliver_t deliver;
+ int buffer_idx;
+ unsigned int nr_events;
+ enum oe_flush last_flush_type;
+ u32 nr_unordered_events;
+ bool copy_on_queue;
};

int ordered_events__queue(struct ordered_events *oe, union perf_event *event,
--
2.17.1
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