linux-kernel - Re: [PATCH v3] locking/lockdep: Fix meaningless usages output of lock classes

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Message-ID: <0894c552-41f1-a9dc-a319-67233c751a1f@redhat.com>
Date:   Tue, 29 Jun 2021 10:02:24 -0400
From:   Waiman Long <llong@...hat.com>
To:     Xiongwei Song <sxwjean@...com>, peterz@...radead.org,
        mingo@...hat.com, will@...nel.org, boqun.feng@...il.com
Cc:     linux-kernel@...r.kernel.org, Xiongwei Song <sxwjean@...il.com>
Subject: Re: [PATCH v3] locking/lockdep: Fix meaningless usages output of lock
 classes

On 6/29/21 9:59 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 with CONFIG_PROVE_LOCKING undefined, we can get the
> results below:
>
> / # cat /proc/lockdep
> all lock classes:
> ffffffff85163290: cgroup_mutex
> ffffffff85154dd8: (console_sem).lock
> ffffffff85154d80: console_lock
> ffffffff85074b58: console_owner_lock
> ffffffff85074ba0: console_owner
> ffffffff85066d60: cpu_hotplug_lock
>
> a class key and the relevant class name each line.
>
> Signed-off-by: Xiongwei Song <sxwjean@...il.com>
> ---
>
> v3: Improve commit log. Thank Longman very much for the comments.
> v2: https://lkml.org/lkml/2021/6/28/1549
>
> ---
>   kernel/locking/lockdep_proc.c | 26 ++++++++++++++------------
>   1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
> index 806978314496..b8d9a050c337 100644
> --- a/kernel/locking/lockdep_proc.c
> +++ b/kernel/locking/lockdep_proc.c
> @@ -70,26 +70,28 @@ 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");
>   	}
> -	seq_puts(m, "\n");
>   
>   	return 0;
>   }

Looks good to me.

Acked-by: Waiman Long <longman@...hat.com>