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

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Message-ID: <162547161509.395.12111477332753183993.tip-bot2@tip-bot2>
Date:   Mon, 05 Jul 2021 07:53:35 -0000
From:   "tip-bot2 for Xiongwei Song" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Xiongwei Song <sxwjean@...il.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/urgent] locking/lockdep: Fix meaningless usages output
 of lock classes

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     a23fb0cfa911423327e5a2089d33ab6cddc6a6aa
Gitweb:        https://git.kernel.org/tip/a23fb0cfa911423327e5a2089d33ab6cddc6a6aa
Author:        Xiongwei Song <sxwjean@...il.com>
AuthorDate:    Tue, 29 Jun 2021 21:59:16 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 02 Jul 2021 15:58:26 +02:00

locking/lockdep: Fix meaningless usages output of lock classes

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Waiman Long <longman@...hat.com>
Link: https://lore.kernel.org/r/20210629135916.308210-1-sxwjean@me.com
---
 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 8069783..b8d9a05 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;
 }