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

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Date:   Sun, 27 Jun 2021 22:23:20 +0800
From:   Xiongwei Song <sxwjean@...com>
To:     peterz@...radead.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, boqun.feng@...il.com,
        linux-kernel@...r.kernel.org
Cc:     Xiongwei Song <sxwjean@...il.com>
Subject: [PATCH] locking/lockdep: Fix meaningless usages output of lock classes

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
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@...il.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