Re: [PATCH v4 01/53] perf comm: Use regular mutex

[Ian Rogers]

On Sun, Nov 5, 2023 at 9:32 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> Hi Ian,
>
> On Thu, Nov 2, 2023 at 10:58 AM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > The rwsem is only after used for writing so switch to a mutex that has
> > better error checking.
>
> Hmm.. ok.  It doesn't make sense to use rwsem without readers.
>
> >
> > Fixes: 7a8f349e9d14 ("perf rwsem: Add debug mode that uses a mutex")
>
> But I'm not sure this is a fix.  Other than that,

Thanks Namhyung, it fixes the case that you enable RWS_ERRORCHECK in
rwsem.h as the rwsem static initialization is wrong for a mutex.

Ian

> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
>
> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
>
> Thanks,
> Namhyung
>
>
> > ---
> >  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,};
> >
> >  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;
> >  }
> > --
> > 2.42.0.869.gea05f2083d-goog
> >