Hello,
On Tue, Mar 2, 2021 at 11:35 AM Dmitry Safonov <d...@arista.com> wrote:
>
> __cmd_diff() sets result of perf_session__new() to d->session.
> In case of failure, it's errno and perf-diff may crash with:
> failed to open perf.data: Permission denied
> Failed to open perf.data
> Segmentation fault (core dumped)
>
> From the coredump:
> 0 0x00005569a62b5955 in auxtrace__free (session=0xffffffffffffffff)
> at util/auxtrace.c:2681
> 1 0x00005569a626b37d in perf_session__delete (session=0xffffffffffffffff)
> at util/session.c:295
> 2 perf_session__delete (session=0xffffffffffffffff) at util/session.c:291
> 3 0x00005569a618008a in __cmd_diff () at builtin-diff.c:1239
> 4 cmd_diff (argc=<optimized out>, argv=<optimized out>) at
> builtin-diff.c:2011
> [..]
>
> Funny enough, it won't always crash. For me it crashes only if failed
> file is second in cmd-line: the reason is that cmd_diff() check files for
> branch-stacks [in check_file_brstack()] and if the first file doesn't
> have brstacks, it doesn't proceed to try open other files from cmd-line.
>
> Check d->session before calling perf_session__delete().
>
> Another solution would be assigning to temporary variable, checking it,
> but I find it easier to follow with IS_ERR() check in the same function.
> After some time it's still obvious why the check is needed, and with
> temp variable it's possible to make the same mistake.
>
> Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
> Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Jiri Olsa <jo...@redhat.com>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Namhyung Kim <namhy...@kernel.org>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Signed-off-by: Dmitry Safonov <d...@arista.com>
Acked-by: Namhyung Kim <namhy...@kernel.org>
Thanks,
Namhyung
> ---
> tools/perf/builtin-diff.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
> index cefc71506409..b0c57e55052d 100644
> --- a/tools/perf/builtin-diff.c
> +++ b/tools/perf/builtin-diff.c
> @@ -1236,7 +1236,8 @@ static int __cmd_diff(void)
>
> out_delete:
> data__for_each_file(i, d) {
> - perf_session__delete(d->session);
> + if (!IS_ERR(d->session))
> + perf_session__delete(d->session);
> data__free(d);
> }
>
> --
> 2.30.1
>
