Re: [PATCH 2/2] perf iostat: Fix Segmentation fault from NULL 'struct perf_counts_values *'

Arnaldo Carvalho de Melo
2021-09-27T12:42:54Z

Em Mon, Sep 27, 2021 at 04:11:15PM +0800, Like Xu escreveu:
> From: Like Xu <likexu@tencent.com>
>
> If the perf-iostat user specifies two or more iio_root_ports and
> also specifies the cpu(s) by -C which is not *connected to all*
> the above iio ports, the iostat_print_metric() will run into trouble:
>
> For example:
>
> $ perf iostat list
> S0-uncore_iio_0<0000:16>
> S1-uncore_iio_0<0000:97> # <--- CPU 1 is located in the socket S0
>
> $ perf iostat 0000:16,0000:97 -C 1 -- ls
> port Inbound Read(MB) Inbound Write(MB) Outbound Read(MB) Outbound
> Write(MB) ../perf-iostat: line 12: 104418 Segmentation fault
> (core dumped) perf stat --iostat$DELIMITER$*
>
> The core-dump stack says, in the above corner case, the returned
> (struct perf_counts_values *) count will be NULL, and the caller
> iostat_print_metric() apparently doesn't not handle this case.
>
> 433 struct perf_counts_values *count = perf_counts(evsel->counts, die, 0);
> 434
> 435 if (count->run && count->ena) {
> (gdb) p count
> $1 = (struct perf_counts_values *) 0x0
>
> The deeper reason is that there are actually no statistics from the user
> specified pair "iostat 0000:X, -C (disconnected) Y ", but let's fix it with
> minimum cost by adding a NULL check in the user space.

Added:

Fixes: f9ed693e8bc0e7de ("perf stat: Enable iostat mode for x86 platforms")

Please do that next time,

- Arnaldo

> Signed-off-by: Like Xu <likexu@tencent.com>
> ---
> tools/perf/arch/x86/util/iostat.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/arch/x86/util/iostat.c b/tools/perf/arch/x86/util/iostat.c
> index eeafe97b8105..792cd75ade33 100644
> --- a/tools/perf/arch/x86/util/iostat.c
> +++ b/tools/perf/arch/x86/util/iostat.c
> @@ -432,7 +432,7 @@ void iostat_print_metric(struct perf_stat_config *config, struct evsel *evsel,
> u8 die = ((struct iio_root_port *)evsel->priv)->die;
> struct perf_counts_values *count = perf_counts(evsel->counts, die, 0);
>
> - if (count->run && count->ena) {
> + if (count && count->run && count->ena) {
> if (evsel->prev_raw_counts && !out->force_header) {
> struct perf_counts_values *prev_count =
> perf_counts(evsel->prev_raw_counts, die, 0);
> --
> 2.32.0

--

- Arnaldo