linux-kernel - [PATCH 1/3] lockdep: Assign lock keys on registration

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Date:   Wed, 17 Jan 2018 07:14:12 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] lockdep: Assign lock keys on registration

From: Matthew Wilcox <mawilcox@...rosoft.com>

Lockdep was assigning lock keys when a lock was looked up.  This is
unnecessary; if the lock has never been registered then we know it is
not locked.  It also complicates the calling convention.  Switch to
assigning the lock key in register_lock_class().

Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
---
 kernel/locking/lockdep.c | 76 +++++++++++++++++++++++++-----------------------
 1 file changed, 40 insertions(+), 36 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5fa1324a4f29..472547dd45c3 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -647,18 +647,12 @@ static int count_matching_names(struct lock_class *new_class)
 	return count + 1;
 }
 
-/*
- * Register a lock's class in the hash-table, if the class is not present
- * yet. Otherwise we look it up. We cache the result in the lock object
- * itself, so actual lookup of the hash should be once per lock object.
- */
 static inline struct lock_class *
 look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
 {
 	struct lockdep_subclass_key *key;
 	struct hlist_head *hash_head;
 	struct lock_class *class;
-	bool is_static = false;
 
 	if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
 		debug_locks_off();
@@ -671,24 +665,11 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
 	}
 
 	/*
-	 * Static locks do not have their class-keys yet - for them the key
-	 * is the lock object itself. If the lock is in the per cpu area,
-	 * the canonical address of the lock (per cpu offset removed) is
-	 * used.
+	 * If it is not initialised then it has never been locked,
+	 * so it won't be present in the hash table.
 	 */
-	if (unlikely(!lock->key)) {
-		unsigned long can_addr, addr = (unsigned long)lock;
-
-		if (__is_kernel_percpu_address(addr, &can_addr))
-			lock->key = (void *)can_addr;
-		else if (__is_module_percpu_address(addr, &can_addr))
-			lock->key = (void *)can_addr;
-		else if (static_obj(lock))
-			lock->key = (void *)lock;
-		else
-			return ERR_PTR(-EINVAL);
-		is_static = true;
-	}
+	if (unlikely(!lock->key))
+		return NULL;
 
 	/*
 	 * NOTE: the class-key must be unique. For dynamic locks, a static
@@ -720,7 +701,35 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
 		}
 	}
 
-	return is_static || static_obj(lock->key) ? NULL : ERR_PTR(-EINVAL);
+	return NULL;
+}
+
+/*
+ * Static locks do not have their class-keys yet - for them the key is
+ * the lock object itself. If the lock is in the per cpu area, the
+ * canonical address of the lock (per cpu offset removed) is used.
+ */
+static bool assign_lock_key(struct lockdep_map *lock)
+{
+	unsigned long can_addr, addr = (unsigned long)lock;
+
+	if (__is_kernel_percpu_address(addr, &can_addr))
+		lock->key = (void *)can_addr;
+	else if (__is_module_percpu_address(addr, &can_addr))
+		lock->key = (void *)can_addr;
+	else if (static_obj(lock))
+		lock->key = (void *)lock;
+	else {
+		/* Debug-check: all keys must be persistent! */
+		debug_locks_off();
+		pr_err("INFO: trying to register non-static key.\n");
+		pr_err("the code is fine but needs lockdep annotation.\n");
+		pr_err("turning off the locking correctness validator.\n");
+		dump_stack();
+		return false;
+	}
+
+	return true;
 }
 
 /*
@@ -738,18 +747,13 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 	DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
 	class = look_up_lock_class(lock, subclass);
-	if (likely(!IS_ERR_OR_NULL(class)))
+	if (likely(class))
 		goto out_set_class_cache;
 
-	/*
-	 * Debug-check: all keys must be persistent!
-	 */
-	if (IS_ERR(class)) {
-		debug_locks_off();
-		printk("INFO: trying to register non-static key.\n");
-		printk("the code is fine but needs lockdep annotation.\n");
-		printk("turning off the locking correctness validator.\n");
-		dump_stack();
+	if (!lock->key) {
+		if (!assign_lock_key(lock))
+			return NULL;
+	} else if (!static_obj(lock->key)) {
 		return NULL;
 	}
 
@@ -3498,7 +3502,7 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
 		 * Clearly if the lock hasn't been acquired _ever_, we're not
 		 * holding it either, so report failure.
 		 */
-		if (IS_ERR_OR_NULL(class))
+		if (!class)
 			return 0;
 
 		/*
@@ -4294,7 +4298,7 @@ void lockdep_reset_lock(struct lockdep_map *lock)
 		 * If the class exists we look it up and zap it:
 		 */
 		class = look_up_lock_class(lock, j);
-		if (!IS_ERR_OR_NULL(class))
+		if (class)
 			zap_class(class);
 	}
 	/*
-- 
2.15.1