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    SubjectRe: [PATCH v5 01/50] perf comm: Use regular mutex
    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
    >

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