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Subject[PATCH 8/8] locking/lockdep: Consider zapped locks when printing lock chains in /proc
Date
It is not rare to spot empty lock chains in /proc/lockdep_chains, where only
shows irq_context but not the locks, which is useless and makes people
confused.

This happens because the chained lock classes are freeed, so consider this
when printing the lock chains.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
kernel/locking/lockdep_proc.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 3d31f9b..47a6f4f 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -127,7 +127,7 @@ static int lc_show(struct seq_file *m, void *v)
{
struct lock_chain *chain = v;
struct lock_class *class;
- int i;
+ int i, nr_locks = 0;

if (v == SEQ_START_TOKEN) {
if (nr_chain_hlocks > MAX_LOCKDEP_CHAIN_HLOCKS)
@@ -136,18 +136,28 @@ static int lc_show(struct seq_file *m, void *v)
return 0;
}

- seq_printf(m, "irq_context: %d\n", chain->irq_context);
-
for (i = 0; i < chain->depth; i++) {
class = lock_chain_get_class(chain, i);
+ /*
+ * Is this lock class zapped?
+ */
if (!class->key)
continue;

+ if (!nr_locks++)
+ seq_printf(m, "irq_context: %d\n", chain->irq_context);
+
seq_printf(m, "[%p] ", class->key);
print_name(m, class);
seq_puts(m, "\n");
}
- seq_puts(m, "\n");
+
+ if (nr_locks) {
+ if (nr_locks != chain->depth)
+ seq_printf(m, "(chain has %d zapped classes)\n",
+ chain->depth - nr_locks);
+ seq_puts(m, "\n");
+ }

return 0;
}
--
1.8.3.1
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