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From:   Xiongwei Song <sxwjean@gmail.com>
Date:   Mon, 28 Jun 2021 11:19:06 +0800
Message-ID: <CAEVVKH8bb1Y5hLttmUFR_gAkA5p=SjcCqMvUoh-=iZ6sVaYPpA@mail.gmail.com>
Subject: Re: [PATCH] locking/lockdep: Fix meaningless usages output of lock classes
To:     Xiongwei Song <sxwjean@me.com>
Cc:     peterz@infradead.org, mingo@redhat.com, will@kernel.org,
        longman@redhat.com, Boqun Feng <boqun.feng@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Please ignore this patch, it's not good. I will improve it.

Regards,
Xiongwei

On Sun, Jun 27, 2021 at 10:23 PM Xiongwei Song <sxwjean@me.com> wrote:
>
> From: Xiongwei Song <sxwjean@gmail.com>
>
> When enabling CONFIG_LOCK_STAT, then CONFIG_LOCKDEP is forcedly enabled.
> We can get output from /proc/lockdep, which currently includes usages of
> classes. But the usages of classes 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 it defined section.
>
> Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> ---
>  kernel/locking/lockdep_proc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
> index 806978314496..1b1103ee7dc6 100644
> --- a/kernel/locking/lockdep_proc.c
> +++ b/kernel/locking/lockdep_proc.c
> @@ -73,10 +73,11 @@ static int l_show(struct seq_file *m, void *v)
>  #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
>
>         get_usage_chars(class, usage);
>         seq_printf(m, " %s", usage);
> +#endif
> +
>
>         seq_printf(m, ": ");
>         print_name(m, class);
> --
> 2.30.2
>