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Message-ID: <CAP-5=fXgy95LsYLbbWN85prBs43jvGehOcwYFK-ZK2cOqCyPJA@mail.gmail.com>
Date: Sun, 5 Nov 2023 13:35:42 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
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liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v4 01/53] perf comm: Use regular mutex
On Sun, Nov 5, 2023 at 9:32 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hi Ian,
>
> On Thu, Nov 2, 2023 at 10:58 AM Ian Rogers <irogers@...gle.com> 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@...gle.com>
>
> Acked-by: Namhyung Kim <namhyung@...nel.org>
>
> 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
> >
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