linux-kernel - Re: [PATCH v2] locking/lockdep: Fix meaningless usages output of lock classes

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Message-ID: <CAEVVKH-rJCutaHJ3WzssSBPmd_TDk5kECWXWtKpSZqXe0UM-iQ@mail.gmail.com>
Date:   Tue, 29 Jun 2021 10:52:41 +0800
From:   Xiongwei Song <sxwjean@...il.com>
To:     Waiman Long <llong@...hat.com>
Cc:     Xiongwei Song <sxwjean@...com>, peterz@...radead.org,
        mingo@...hat.com, will@...nel.org,
        Boqun Feng <boqun.feng@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] locking/lockdep: Fix meaningless usages output of lock classes

On Tue, Jun 29, 2021 at 5:17 AM Waiman Long <llong@...hat.com> wrote:
>
> On 6/28/21 11:17 AM, Xiongwei Song wrote:
> > From: Xiongwei Song <sxwjean@...il.com>
> >
> > When enabling CONFIG_LOCK_STAT, then CONFIG_LOCKDEP is forcedly enabled.
> > We can get output from /proc/lockdep, which currently includes usages of
> > lock classes. But the usages are meaningless, see the output below:
> >
> > / # cat /proc/lockdep
> > all lock classes:
> > ffffffff9af63350 ....: cgroup_mutex
> >
> > ffffffff9af54eb8 ....: (console_sem).lock
> >
> > ffffffff9af54e60 ....: console_lock
> >
> > ffffffff9ae74c38 ....: console_owner_lock
> >
> > ffffffff9ae74c80 ....: console_owner
> >
> > ffffffff9ae66e60 ....: cpu_hotplug_lock
> >
> > Only one usage context for each lock, this is because each usage is only
> > changed in mark_lock() that is in CONFIG_PROVE_LOCKING defined section,
> > however in the test situation, it's not.
> >
> > The fix is to move the usages reading and seq_print from
> > CONFIG_PROVE_LOCKING undefined setcion to its defined section. Also,
> > locks_after list of lock_class is empty when CONFIG_PROVE_LOCKING
> > undefined, so do the same thing as what have done for usages of lock
> > classes.
> With this patch, CONFIG_LOCKDEP without CONFIG_PROVE_LOCKING will make
> /proc/lockdep displays just the list of lock classes with their
> associated lock keys. I think it is worth explicitly saying that in the
> commit log.

Make sense. Will update.

> > Signed-off-by: Xiongwei Song <sxwjean@...il.com>
> > ---
> >   kernel/locking/lockdep_proc.c | 24 +++++++++++++-----------
> >   1 file changed, 13 insertions(+), 11 deletions(-)
> >
> > diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
> > index 806978314496..a1ec2652d492 100644
> > --- a/kernel/locking/lockdep_proc.c
> > +++ b/kernel/locking/lockdep_proc.c
> > @@ -70,23 +70,25 @@ static int l_show(struct seq_file *m, void *v)
> >   #ifdef CONFIG_DEBUG_LOCKDEP
> >       seq_printf(m, " OPS:%8ld", debug_class_ops_read(class));
> >   #endif
> > -#ifdef CONFIG_PROVE_LOCKING
> > -     seq_printf(m, " FD:%5ld", lockdep_count_forward_deps(class));
> > -     seq_printf(m, " BD:%5ld", lockdep_count_backward_deps(class));
> > -#endif
> > +     if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
> > +             seq_printf(m, " FD:%5ld", lockdep_count_forward_deps(class));
> > +             seq_printf(m, " BD:%5ld", lockdep_count_backward_deps(class));
> >
> > -     get_usage_chars(class, usage);
> > -     seq_printf(m, " %s", usage);
> > +             get_usage_chars(class, usage);
> > +             seq_printf(m, " %s", usage);
> > +     }
> >
> >       seq_printf(m, ": ");
> >       print_name(m, class);
> >       seq_puts(m, "\n");
> >
> > -     list_for_each_entry(entry, &class->locks_after, entry) {
> > -             if (entry->distance == 1) {
> > -                     seq_printf(m, " -> [%p] ", entry->class->key);
> > -                     print_name(m, entry->class);
> > -                     seq_puts(m, "\n");
> > +     if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
> > +             list_for_each_entry(entry, &class->locks_after, entry) {
> > +                     if (entry->distance == 1) {
> > +                             seq_printf(m, " -> [%p] ", entry->class->key);
> > +                             print_name(m, entry->class);
> > +                             seq_puts(m, "\n");
> > +                     }
> >               }
> >       }
> >       seq_puts(m, "\n");
>
> Maybe you can remove the blank lines in this case by moving the last
> seq_puts() inside the if loop. The blank lines are not really needed
> without the associated locks_after information.

Yeah, I agree. Thank you.

Regards,
Xiongwei

> Cheers,
> Longman
>