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SubjectRe: [PATCHv3] perf tools: Add struct ordered_events_buffer layer
Jiri,

On Sun, Sep 2, 2018 at 7:47 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Mon, Aug 27, 2018 at 07:05:43PM +0200, Jiri Olsa wrote:
> > On Mon, Aug 27, 2018 at 08:24:56AM -0700, Stephane Eranian wrote:
> >
> > SNIP
> >
> > > > - /* 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);
> > >
> > >
> > > I am wondering about the usefulness of returning a new_event with
> > > new_event->event = NULL
> > > in this case. Don't you need new_event->event? If so, then you need return NULL.
> >
> > yep, that's a bug.. with new being NULL in here,
> > we'd get a crash anyway.. so 'return NULL;' it is
> >
> > SNIP
> >
> > > > + * yet, we need to free only allocated ones ...
> > > > + */
> > > > + list_del(&oe->buffer->list);
> > > > + ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
> > > > +
> > > > + /* ... and continue with the rest */
> > > > + list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {
> > > > + list_del(&buffer->list);
> > > > + ordered_events_buffer__free(buffer, MAX_SAMPLE_BUFFER, oe);
> > >
> > >
> > > Here you are saying that if it is on the to_free list and not the
> > > current buffer, then necessarily
> > > all the entries have been used and it is safe to use
> > > MAX_SAMPLE_BUFFER. Is that right?
> >
> > yes, at this point they either holds an event or NULL
> > so it's free to call __free_dup_event on it
> >
> > thanks, v3 attached
> >
> > added also Namhyung's ack, as the 'return NULL' change wasn't
> > related to the v2 changes
> >

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@google.com>

> jirka
>
> Stephane,
> any comments to v3 version?
>
> 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>
> > Acked-by: Namhyung Kim <namhyung@kernel.org>
> > 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 | 83 +++++++++++++++++++++++++++-----
> > tools/perf/util/ordered-events.h | 37 ++++++++------
> > 2 files changed, 91 insertions(+), 29 deletions(-)
> >
> > diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
> > index bad9e0296e9a..87171e8fd70d 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)
> > @@ -100,15 +106,43 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
> > if (!new_event)
> > return NULL;
> >
> > + /*
> > + * We maintain following scheme of buffers for ordered
> > + * event allocation:
> > + *
> > + * to_free list -> buffer1 (64K)
> > + * buffer2 (64K)
> > + * ...
> > + *
> > + * Each buffer keeps an array of ordered events objects:
> > + * buffer -> event[0]
> > + * event[1]
> > + * ...
> > + *
> > + * Each allocated ordered event is linked to one of
> > + * following lists:
> > + * - time ordered list 'events'
> > + * - list of currently removed events 'cache'
> > + *
> > + * Allocation of the ordered event uses following order
> > + * to get the memory:
> > + * - use recently removed object from 'cache' list
> > + * - use available object in current allocation buffer
> > + * - allocate new buffer if the current buffer is full
> > + *
> > + * Removal of ordered event object moves it from events to
> > + * the cache list.
> > + */
> > 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;
> > + 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) {
> > @@ -122,11 +156,11 @@ 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);
> > + return NULL;
> > }
> >
> > new->event = new_event;
> > @@ -300,15 +334,38 @@ 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,
> > + unsigned int max, struct ordered_events *oe)
> > +{
> > + if (oe->copy_on_queue) {
> > + unsigned int i;
> > +
> > + for (i = 0; i < max; 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);
> > + if (list_empty(&oe->to_free))
> > + return;
> > +
> > + /*
> > + * Current buffer might not have all the events allocated
> > + * yet, we need to free only allocated ones ...
> > + */
> > + list_del(&oe->buffer->list);
> > + ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
> > +
> > + /* ... and continue with the rest */
> > + list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {
> > + list_del(&buffer->list);
> > + ordered_events_buffer__free(buffer, MAX_SAMPLE_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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