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From:   Ian Rogers <irogers@google.com>
Date:   Mon, 27 Nov 2023 10:59:19 -0800
Message-ID: <CAP-5=fWpNUPfZ6Qs45kw1BkDB0erOu0whzaV0VsYtkLuJhGpAg@mail.gmail.com>
Subject: Re: [PATCH v4 01/53] perf comm: Use regular mutex
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Nick Terrell <terrelln@fb.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kajol Jain <kjain@linux.ibm.com>,
        Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        "Steinar H. Gunderson" <sesse@google.com>,
        Liam Howlett <liam.howlett@oracle.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Colin Ian King <colin.i.king@gmail.com>,
        Dmitrii Dolgov <9erthalion6@gmail.com>,
        Yang Jihong <yangjihong1@huawei.com>,
        Ming Wang <wangming01@loongson.cn>,
        James Clark <james.clark@arm.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Sean Christopherson <seanjc@google.com>,
        Leo Yan <leo.yan@linaro.org>,
        Ravi Bangoria <ravi.bangoria@amd.com>,
        German Gomez <german.gomez@arm.com>,
        Changbin Du <changbin.du@huawei.com>,
        Paolo Bonzini <pbonzini@redhat.com>, Li Dong <lidong@vivo.com>,
        Sandipan Das <sandipan.das@amd.com>,
        liuwenyu <liuwenyu7@huawei.com>, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org
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On Sun, Nov 5, 2023 at 7:59=E2=80=AFPM Namhyung Kim <namhyung@kernel.org> w=
rote:
>
> On Sun, Nov 5, 2023 at 1:35=E2=80=AFPM Ian Rogers <irogers@google.com> wr=
ote:
> >
> > On Sun, Nov 5, 2023 at 9:32=E2=80=AFAM Namhyung Kim <namhyung@kernel.or=
g> wrote:
> > >
> > > Hi Ian,
> > >
> > > On Thu, Nov 2, 2023 at 10:58=E2=80=AFAM Ian Rogers <irogers@google.co=
m> 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.
>
> Sounds like we need a separate fix.  Maybe you need to
> add a static initializer macro depending on the config.

Agreed, but the only use would be here and switching this case to a
mutex gives extra error checking such as the mutex being taken
recursively. Given that, I prefer the existing change and the static
initializer for rwsem can be a follow up when needed.

Thanks,
Ian

> Thanks,
> Namhyung