Re: [PATCH] perf record: Fix memory leak in vDSO

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Mar 15, 2021 at 01:56:41PM +0900, Namhyung Kim wrote:
> I got several memory leak reports from Asan with a simple command.  It
> was because VDSO is not released due to the refcount.  Like in
> __dsos_addnew_id(), it should put the refcount after adding to the list.
> 
>   $ perf record true
>   [ perf record: Woken up 1 times to write data ]
>   [ perf record: Captured and wrote 0.030 MB perf.data (10 samples) ]
> 
>   =================================================================
>   ==692599==ERROR: LeakSanitizer: detected memory leaks
> 
>   Direct leak of 439 byte(s) in 1 object(s) allocated from:
>     #0 0x7fea52341037 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
>     #1 0x559bce4aa8ee in dso__new_id util/dso.c:1256
>     #2 0x559bce59245a in __machine__addnew_vdso util/vdso.c:132
>     #3 0x559bce59245a in machine__findnew_vdso util/vdso.c:347
>     #4 0x559bce50826c in map__new util/map.c:175
>     #5 0x559bce503c92 in machine__process_mmap2_event util/machine.c:1787
>     #6 0x559bce512f6b in machines__deliver_event util/session.c:1481
>     #7 0x559bce515107 in perf_session__deliver_event util/session.c:1551
>     #8 0x559bce51d4d2 in do_flush util/ordered-events.c:244
>     #9 0x559bce51d4d2 in __ordered_events__flush util/ordered-events.c:323
>     #10 0x559bce519bea in __perf_session__process_events util/session.c:2268
>     #11 0x559bce519bea in perf_session__process_events util/session.c:2297
>     #12 0x559bce2e7a52 in process_buildids /home/namhyung/project/linux/tools/perf/builtin-record.c:1017
>     #13 0x559bce2e7a52 in record__finish_output /home/namhyung/project/linux/tools/perf/builtin-record.c:1234
>     #14 0x559bce2ed4f6 in __cmd_record /home/namhyung/project/linux/tools/perf/builtin-record.c:2026
>     #15 0x559bce2ed4f6 in cmd_record /home/namhyung/project/linux/tools/perf/builtin-record.c:2858
>     #16 0x559bce422db4 in run_builtin /home/namhyung/project/linux/tools/perf/perf.c:313
>     #17 0x559bce2acac8 in handle_internal_command /home/namhyung/project/linux/tools/perf/perf.c:365
>     #18 0x559bce2acac8 in run_argv /home/namhyung/project/linux/tools/perf/perf.c:409
>     #19 0x559bce2acac8 in main /home/namhyung/project/linux/tools/perf/perf.c:539
>     #20 0x7fea51e76d09 in __libc_start_main ../csu/libc-start.c:308
> 
>   Indirect leak of 32 byte(s) in 1 object(s) allocated from:
>     #0 0x7fea52341037 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
>     #1 0x559bce520907 in nsinfo__copy util/namespaces.c:169
>     #2 0x559bce50821b in map__new util/map.c:168
>     #3 0x559bce503c92 in machine__process_mmap2_event util/machine.c:1787
>     #4 0x559bce512f6b in machines__deliver_event util/session.c:1481
>     #5 0x559bce515107 in perf_session__deliver_event util/session.c:1551
>     #6 0x559bce51d4d2 in do_flush util/ordered-events.c:244
>     #7 0x559bce51d4d2 in __ordered_events__flush util/ordered-events.c:323
>     #8 0x559bce519bea in __perf_session__process_events util/session.c:2268
>     #9 0x559bce519bea in perf_session__process_events util/session.c:2297
>     #10 0x559bce2e7a52 in process_buildids /home/namhyung/project/linux/tools/perf/builtin-record.c:1017
>     #11 0x559bce2e7a52 in record__finish_output /home/namhyung/project/linux/tools/perf/builtin-record.c:1234
>     #12 0x559bce2ed4f6 in __cmd_record /home/namhyung/project/linux/tools/perf/builtin-record.c:2026
>     #13 0x559bce2ed4f6 in cmd_record /home/namhyung/project/linux/tools/perf/builtin-record.c:2858
>     #14 0x559bce422db4 in run_builtin /home/namhyung/project/linux/tools/perf/perf.c:313
>     #15 0x559bce2acac8 in handle_internal_command /home/namhyung/project/linux/tools/perf/perf.c:365
>     #16 0x559bce2acac8 in run_argv /home/namhyung/project/linux/tools/perf/perf.c:409
>     #17 0x559bce2acac8 in main /home/namhyung/project/linux/tools/perf/perf.c:539
>     #18 0x7fea51e76d09 in __libc_start_main ../csu/libc-start.c:308
> 
>   SUMMARY: AddressSanitizer: 471 byte(s) leaked in 2 allocation(s).
> 
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/util/vdso.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/util/vdso.c b/tools/perf/util/vdso.c
> index 3cc91ad048ea..43beb169631d 100644
> --- a/tools/perf/util/vdso.c
> +++ b/tools/perf/util/vdso.c
> @@ -133,6 +133,8 @@ static struct dso *__machine__addnew_vdso(struct machine *machine, const char *s
>  	if (dso != NULL) {
>  		__dsos__add(&machine->dsos, dso);
>  		dso__set_long_name(dso, long_name, false);
> +		/* Put dso here because __dsos_add already got it */
> +		dso__put(dso);

from quick look I don't understand why we take refcnt down
right after adding to the list.. it would make sense to me
if dso is not stored elsewhere so we want dsos__exit to
release it.. but it's still stored in map object

I checked and we do extra dso__get in machine__findnew_vdso
(and also in dsos__findnew_id) ... so that one seems to me
like the one we should remove

but I might be missing something, I'll try to check more
deeply later on

jirka