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Subject[PATCH v3] locking/lockdep: Fix meaningless usages output of lock classes
Date
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
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@gmail.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;
}
--
2.30.2
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