linux-kernel - [PATCH 8/8] locking/lockdep: Consider zapped locks when printing lock chains in /proc

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Date:   Tue, 26 Feb 2019 18:03:27 +0800
From:   Yuyang Du <duyuyang@...il.com>
To:     peterz@...radead.org, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, Yuyang Du <duyuyang@...il.com>
Subject: [PATCH 8/8] locking/lockdep: Consider zapped locks when printing lock chains in /proc

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@...il.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