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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Wed, 29 Nov 2023 16:55:52 -0800
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Subject: Re: [PATCH v5 01/50] perf comm: Use regular mutex
To:     Ian Rogers <irogers@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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On Mon, Nov 27, 2023 at 2:09 PM Ian Rogers <irogers@google.com> wrote:
>
> The rwsem is only after used for writing so switch to a mutex that has
> better error checking.
>
> Fixes: 7a8f349e9d14 ("perf rwsem: Add debug mode that uses a mutex")

I think we talked about fixing this separately, no?


> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/comm.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c
> index afb8d4fd2644..4ae7bc2aa9a6 100644
> --- a/tools/perf/util/comm.c
> +++ b/tools/perf/util/comm.c
> @@ -17,7 +17,7 @@ struct comm_str {
>
>  /* Should perhaps be moved to struct machine */
>  static struct rb_root comm_str_root;
> -static struct rw_semaphore comm_str_lock = {.lock = PTHREAD_RWLOCK_INITIALIZER,};
> +static struct mutex comm_str_lock = {.lock = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP,};

IIUC it has a problem with musl libc.  Actually I think it's better to
hide the field and the pthread initializer under some macro like
MUTEX_INITIALIZER or DEFINE_MUTEX() like in the kernel.

Thanks,
Namhyung

>
>  static struct comm_str *comm_str__get(struct comm_str *cs)
>  {
> @@ -30,9 +30,9 @@ static struct comm_str *comm_str__get(struct comm_str *cs)
>  static void comm_str__put(struct comm_str *cs)
>  {
>         if (cs && refcount_dec_and_test(&cs->refcnt)) {
> -               down_write(&comm_str_lock);
> +               mutex_lock(&comm_str_lock);
>                 rb_erase(&cs->rb_node, &comm_str_root);
> -               up_write(&comm_str_lock);
> +               mutex_unlock(&comm_str_lock);
>                 zfree(&cs->str);
>                 free(cs);
>         }
> @@ -98,9 +98,9 @@ static struct comm_str *comm_str__findnew(const char *str, struct rb_root *root)
>  {
>         struct comm_str *cs;
>
> -       down_write(&comm_str_lock);
> +       mutex_lock(&comm_str_lock);
>         cs = __comm_str__findnew(str, root);
> -       up_write(&comm_str_lock);
> +       mutex_unlock(&comm_str_lock);
>
>         return cs;
>  }
> --
> 2.43.0.rc1.413.gea7ed67945-goog
>