Re: [PATCH 6/7] hw_breakpoint_test: fix test_many_cpus failure on large systems

[Marco Elver]

On Thu, 14 May 2026 at 07:08, Jia He <justin.he@xxxxxxx> wrote:
>
> On systems with many CPUs (e.g. 128 cores x 4 HW breakpoint slots =
> 512 = MAX_TEST_BREAKPOINTS), test_many_cpus() advances idx to
> MAX_TEST_BREAKPOINTS after the last fill_bp_slots(). The subsequent
> register_test_bp() call hits WARN_ON(idx >= MAX_TEST_BREAKPOINTS),
> returns NULL, and the -ENOSPC expectation fails.
>
> Bail out of the loop when idx reaches the limit. Earlier iterations
> already validate the NOSPC path on other CPUs.
>
> To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> To: Ingo Molnar <mingo@xxxxxxxxxx>
> To: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> To: Namhyung Kim <namhyung@xxxxxxxxxx>
> To: Mark Rutland <mark.rutland@xxxxxxx>
> To: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> To: Jiri Olsa <jolsa@xxxxxxxxxx>
> To: Ian Rogers <irogers@xxxxxxxxxx>
> To: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> To: James Clark <james.clark@xxxxxxxxxx>
> Cc: linux-perf-users@xxxxxxxxxxxxxxx
>
> Signed-off-by: Jia He <justin.he@xxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
>  kernel/events/hw_breakpoint_test.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/events/hw_breakpoint_test.c b/kernel/events/hw_breakpoint_test.c
> index 2cfeeecf8de9..943d040d2224 100644
> --- a/kernel/events/hw_breakpoint_test.c
> +++ b/kernel/events/hw_breakpoint_test.c
> @@ -137,6 +137,9 @@ static void test_many_cpus(struct kunit *test)
>         for_each_online_cpu(cpu) {
>                 bool do_continue = fill_bp_slots(test, &idx, cpu, NULL, 0);
>
> +               if (idx >= MAX_TEST_BREAKPOINTS)
> +                       break;
> +
>                 TEST_EXPECT_NOSPC(register_test_bp(cpu, NULL, idx));
>                 if (!do_continue)
>                         break;
> --
> 2.34.1
>