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From:   Yuyang Du <duyuyang@gmail.com>
To:     peterz@infradead.org, will.deacon@arm.com, mingo@kernel.org
Cc:     bvanassche@acm.org, ming.lei@redhat.com,
        linux-kernel@vger.kernel.org, joe@perches.com,
        Yuyang Du <duyuyang@gmail.com>
Subject: [PATCH v3 15/18] locking/lockdep: Avoid constant checks in __bfs by using offset reference
Date:   Thu, 21 Mar 2019 15:57:22 +0800
Message-Id: <20190321075725.14054-16-duyuyang@gmail.com>
In-Reply-To: <20190321075725.14054-1-duyuyang@gmail.com>
References: <20190321075725.14054-1-duyuyang@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In search of a dependency in the lock graph, there is contant checks for
forward or backward search. Directly reference the field offset of the
struct that differentiates the type of search to avoid those checks.

No functional change.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
 kernel/locking/lockdep.c | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index ad16793..cd6792c 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1376,11 +1376,25 @@ static inline int get_lock_depth(struct lock_list *child)
 	return depth;
 }
 
+/*
+ * Return the forward or backward dependency list.
+ *
+ * @lock:   the lock_list to get its class's dependency list
+ * @offset: the offset to struct lock_class to determine whether it is
+ *          locks_after or locks_before
+ */
+static inline struct list_head *get_dep_list(struct lock_list *lock, int offset)
+{
+	void *lock_class = lock->class;
+
+	return lock_class + offset;
+}
+
 static int __bfs(struct lock_list *source_entry,
 		 void *data,
 		 int (*match)(struct lock_list *entry, void *data),
 		 struct lock_list **target_entry,
-		 int forward)
+		 int offset)
 {
 	struct lock_list *entry;
 	struct lock_list *lock;
@@ -1394,11 +1408,7 @@ static int __bfs(struct lock_list *source_entry,
 		goto exit;
 	}
 
-	if (forward)
-		head = &source_entry->class->locks_after;
-	else
-		head = &source_entry->class->locks_before;
-
+	head = get_dep_list(source_entry, offset);
 	if (list_empty(head))
 		goto exit;
 
@@ -1412,10 +1422,7 @@ static int __bfs(struct lock_list *source_entry,
 			goto exit;
 		}
 
-		if (forward)
-			head = &lock->class->locks_after;
-		else
-			head = &lock->class->locks_before;
+		head = get_dep_list(lock, offset);
 
 		DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
@@ -1448,7 +1455,8 @@ static inline int __bfs_forwards(struct lock_list *src_entry,
 			int (*match)(struct lock_list *entry, void *data),
 			struct lock_list **target_entry)
 {
-	return __bfs(src_entry, data, match, target_entry, 1);
+	return __bfs(src_entry, data, match, target_entry,
+		     offsetof(struct lock_class, locks_after));
 
 }
 
@@ -1457,7 +1465,8 @@ static inline int __bfs_backwards(struct lock_list *src_entry,
 			int (*match)(struct lock_list *entry, void *data),
 			struct lock_list **target_entry)
 {
-	return __bfs(src_entry, data, match, target_entry, 0);
+	return __bfs(src_entry, data, match, target_entry,
+		     offsetof(struct lock_class, locks_before));
 
 }
 
-- 
1.8.3.1