linux-kernel - Re: [PATCH 02/12] cgroup: rstat: Make cgroup_rstat_cpu

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Date:   Tue, 8 Feb 2022 15:51:43 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Byungchul Park <byungchul.park@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Radoslaw Burny <rburny@...gle.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH 02/12] cgroup: rstat: Make cgroup_rstat_cpu_lock name readable

On Tue, Feb 8, 2022 at 11:16 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hi Tejun,
>
> On Tue, Feb 8, 2022 at 10:46 AM Tejun Heo <tj@...nel.org> wrote:
> >
> > On Tue, Feb 08, 2022 at 10:41:58AM -0800, Namhyung Kim wrote:
> > > The raw_spin_lock_init() uses the argument to name its lockdep map.
> > > But passing per_cpu_ptr() macro directly makes it a very very long
> > > name as it expanded like below:
> > >
> > >   ({ do { const void *__vpp_verify = (typeof((&cgroup_rstat_cpu_lock) ...
> > >
> > > Let's fix it by passing a local variable instead.  With this change,
> > > the name now looks like:
> > >
> > >   cgrp_rstat_cpu_lock
> > >
> > > Cc: Tejun Heo <tj@...nel.org>
> > > Cc: Zefan Li <lizefan.x@...edance.com>
> > > Cc: Johannes Weiner <hannes@...xchg.org>
> > > Cc: cgroups@...r.kernel.org
> > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> >
> > Acked-by: Tejun Heo <tj@...nel.org>
>
> Thanks!
>
> >
> > but maybe add a comment explaining what's going on?
>
> Sure, I'll add the comment.

Actually it depends on CONFIG_DEBUG_SPINLOCK.
If it's enabled, the name looks fine.  But if not, the macro
expansion would happen and generate the long name.

Thanks,
Namhyung