[PATCH v7 9/9] lib/dlock-list: Unique lock class key for each allocation call site

[Waiman Long]

Boqun Feng has kindly pointed out that the same lock class key is
used for all the dlock-list allocation. That can be a problem in case
a task need to acquire the locks of more than one dlock-list at the
same time with lockdep enabled.

To avoid this problem, the alloc_dlock_list_heads() function is
changed to use a different lock class key for each of its call sites
in the kernel.

Reported-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 include/linux/dlock-list.h | 16 +++++++++++++++-
 lib/dlock-list.c           | 21 +++++++++------------
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/include/linux/dlock-list.h b/include/linux/dlock-list.h
index 2ba7b4f..02c5f4d 100644
--- a/include/linux/dlock-list.h
+++ b/include/linux/dlock-list.h
@@ -116,9 +116,23 @@ static inline void dlock_list_relock(struct dlock_list_iter *iter)
 /*
  * Allocation and freeing of dlock list
  */
-extern int  alloc_dlock_list_heads(struct dlock_list_heads *dlist, int irqsafe);
+extern int  __alloc_dlock_list_heads(struct dlock_list_heads *dlist,
+				     int irqsafe, struct lock_class_key *key);
 extern void free_dlock_list_heads(struct dlock_list_heads *dlist);
 
+/**
+ * alloc_dlock_list_head - Initialize and allocate the list of head entries.
+ * @dlist  : Pointer to the dlock_list_heads structure to be initialized
+ * @irqsafe: IRQ safe mode flag
+ * Return  : 0 if successful, -ENOMEM if memory allocation error
+ */
+#define alloc_dlock_list_heads(dlist, irqsafe)				\
+({									\
+	static struct lock_class_key _key;				\
+	int _ret = __alloc_dlock_list_heads(dlist, irqsafe, &_key);	\
+	_ret;								\
+})
+
 /*
  * Check if a dlock list is empty or not.
  */
diff --git a/lib/dlock-list.c b/lib/dlock-list.c
index 6ce5c7193..17e182b 100644
--- a/lib/dlock-list.c
+++ b/lib/dlock-list.c
@@ -36,14 +36,6 @@
 static int nr_dlock_lists __read_mostly;
 
 /*
- * As all the locks in the dlock list are dynamically allocated, they need
- * to belong to their own special lock class to avoid warning and stack
- * trace in kernel log when lockdep is enabled. Statically allocated locks
- * don't have this problem.
- */
-static struct lock_class_key dlock_list_key;
-
-/*
  * Initialize cpu2idx mapping table & nr_dlock_lists.
  *
  * It is possible that a dlock-list can be allocated before the cpu2idx is
@@ -98,9 +90,10 @@ static int __init cpu2idx_init(void)
 postcore_initcall(cpu2idx_init);
 
 /**
- * alloc_dlock_list_heads - Initialize and allocate the list of head entries
+ * __alloc_dlock_list_heads - Initialize and allocate the list of head entries
  * @dlist  : Pointer to the dlock_list_heads structure to be initialized
  * @irqsafe: IRQ safe mode flag
+ * @key    : The lock class key to be used for lockdep
  * Return: 0 if successful, -ENOMEM if memory allocation error
  *
  * This function does not allocate the dlock_list_heads structure itself. The
@@ -112,8 +105,12 @@ static int __init cpu2idx_init(void)
  * than necessary allocated is not a problem other than some wasted memory.
  * The extra lists will not be ever used as all the cpu2idx entries will be
  * 0 before initialization.
+ *
+ * Dynamically allocated locks need to have their own special lock class
+ * to avoid lockdep warning.
  */
-int alloc_dlock_list_heads(struct dlock_list_heads *dlist, int irqsafe)
+int __alloc_dlock_list_heads(struct dlock_list_heads *dlist, int irqsafe,
+			     struct lock_class_key *key)
 {
 	int idx, cnt = nr_dlock_lists ? nr_dlock_lists : nr_cpu_ids;
 
@@ -128,11 +125,11 @@ int alloc_dlock_list_heads(struct dlock_list_heads *dlist, int irqsafe)
 		INIT_LIST_HEAD(&head->list);
 		head->lock = __SPIN_LOCK_UNLOCKED(&head->lock);
 		head->irqsafe = irqsafe;
-		lockdep_set_class(&head->lock, &dlock_list_key);
+		lockdep_set_class(&head->lock, key);
 	}
 	return 0;
 }
-EXPORT_SYMBOL(alloc_dlock_list_heads);
+EXPORT_SYMBOL(__alloc_dlock_list_heads);
 
 /**
  * free_dlock_list_heads - Free all the heads entries of the dlock list
-- 
1.8.3.1