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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.
Fixes: f9ed693e8b ("perf stat: Enable iostat mode for x86 platforms")
Signed-off-by: Like Xu <likexu@tencent.com>
Cc: Alexander Antonov <alexander.antonov@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20210927081115.39568-2-likexu@tencent.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
4da8b12188