Re: [PATCH 2/2] perf report: Fix memory leaks in the hierarchy mode

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

On Thu, Mar 06, 2025 at 08:55:05AM -0800, Ian Rogers wrote:
> On Wed, Mar 5, 2025 at 11:51 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > Ian told me that there are many memory leaks in the hierarchy mode.  I
> > can easily reproduce it with the follwing command.
> >
> >   $ make DEBUG=1 EXTRA_CFLAGS=-fsanitize=leak
> >
> >   $ perf record --latency -g -- ./perf test -w thloop
> >
> >   $ perf report -H --stdio
> >   ...
> >   Indirect leak of 168 byte(s) in 21 object(s) allocated from:
> >       #0 0x7f3414c16c65 in malloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:75
> >       #1 0x55ed3602346e in map__get util/map.h:189
> >       #2 0x55ed36024cc4 in hist_entry__init util/hist.c:476
> >       #3 0x55ed36025208 in hist_entry__new util/hist.c:588
> >       #4 0x55ed36027c05 in hierarchy_insert_entry util/hist.c:1587
> >       #5 0x55ed36027e2e in hists__hierarchy_insert_entry util/hist.c:1638
> >       #6 0x55ed36027fa4 in hists__collapse_insert_entry util/hist.c:1685
> >       #7 0x55ed360283e8 in hists__collapse_resort util/hist.c:1776
> >       #8 0x55ed35de0323 in report__collapse_hists /home/namhyung/project/linux/tools/perf/builtin-report.c:735
> >       #9 0x55ed35de15b4 in __cmd_report /home/namhyung/project/linux/tools/perf/builtin-report.c:1119
> >       #10 0x55ed35de43dc in cmd_report /home/namhyung/project/linux/tools/perf/builtin-report.c:1867
> >       #11 0x55ed35e66767 in run_builtin /home/namhyung/project/linux/tools/perf/perf.c:351
> >       #12 0x55ed35e66a0e in handle_internal_command /home/namhyung/project/linux/tools/perf/perf.c:404
> >       #13 0x55ed35e66b67 in run_argv /home/namhyung/project/linux/tools/perf/perf.c:448
> >       #14 0x55ed35e66eb0 in main /home/namhyung/project/linux/tools/perf/perf.c:556
> >       #15 0x7f340ac33d67 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
> >   ...
> >
> >   $ perf report -H --stdio 2>&1 | grep -c '^Indirect leak'
> >   93
> >
> > I found that hist_entry__delete() missed to release child entries in the
> > hierarchy tree (hroot_{in,out}).  It needs to iterate the child entries
> > and call hist_entry__delete() recursively.
> >
> > After this change:
> >
> >   $ perf report -H --stdio 2>&1 | grep -c '^Indirect leak'
> >   0
> >
> > Reported-by: Ian Rogers <irogers@google.com>
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> >  tools/perf/util/hist.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> > index fbf131aeae7ffe9b..bbc6a299b5106c3b 100644
> > --- a/tools/perf/util/hist.c
> > +++ b/tools/perf/util/hist.c
> > @@ -1385,6 +1385,15 @@ void hist_entry__delete(struct hist_entry *he)
> >  {
> >         struct hist_entry_ops *ops = he->ops;
> >
> > +       while (!RB_EMPTY_ROOT(&he->hroot_out.rb_root)) {
> > +               struct rb_node *node = rb_first(&he->hroot_out.rb_root);
> > +               struct hist_entry *child = rb_entry(node, struct hist_entry, rb_node);
> > +
> > +               rb_erase_init(node, &he->hroot_out.rb_root);
> > +
> > +               hist_entry__delete(child);
> > +       }
> 
> Thanks for the fix! A nit, iterating the rbtree of N nodes and calling
> erase on the first entry, an O(log N) operation, means this is a O(N *
> log N). rbtree.h has rbtree_postorder_for_each_entry_safe:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/include/linux/rbtree.h?h=perf-tools-next#n81
> ```
>  * rbtree_postorder_for_each_entry_safe - iterate in post-order over rb_root of
>  * given type allowing the backing memory of @pos to be invalidated
> ```
> which is O(N). I think this code would be better something like:
> ```
> struct hist_entry *pos, *tmp;
> rbtree_postorder_for_each_entry_safe(pos, tmp, he->hroot_out.rb_root, rb_node)
>         hist_entry__delete(pos);
> ```

Thanks for your review!  I was wondering if there's something like this.
Will update with that.

Thanks,
Namhyung