[PATCH v2 3/5] workqueue: Add interface for user-defined workqueue lockdep map

[Matthew Brost]

Add an interface for a user-defined workqueue lockdep map, which is
helpful when multiple workqueues are created for the same purpose. This
also helps avoid leaking lockdep maps on each workqueue creation.

Implement a new internal workqueue flag, __WQ_USER_OWNED_LOCKDEP, to
indicate that the user will set up the workqueue lockdep map using the
new function alloc_workqueue_lockdep_map. Also add helper macro
alloc_ordered_workqueue_lockdep_map.

v2:
 - Add alloc_workqueue_lockdep_map (Tejun)

Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
 include/linux/workqueue.h | 25 +++++++++++++++++++++++++
 kernel/workqueue.c        | 28 ++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index d9968bfc8eac..1707870ef7c5 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -406,6 +406,7 @@ enum wq_flags {
 	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
 	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
 	__WQ_LEGACY		= 1 << 18, /* internal: create*_workqueue() */
+	__WQ_USER_OWNED_LOCKDEP	= 1 << 19, /* internal: workqueue has user owned lockdep map */
 
 	/* BH wq only allows the following flags */
 	__WQ_BH_ALLOWS		= WQ_BH | WQ_HIGHPRI,
@@ -507,6 +508,30 @@ void workqueue_softirq_dead(unsigned int cpu);
 __printf(1, 4) struct workqueue_struct *
 alloc_workqueue(const char *fmt, unsigned int flags, int max_active, ...);
 
+#ifdef CONFIG_LOCKDEP
+/**
+ * alloc_workqueue_lockdep_map - allocate a workqueue with user-defined lockdep_map
+ * @fmt: printf format for the name of the workqueue
+ * @flags: WQ_* flags
+ * @max_active: max in-flight work items, 0 for default
+ * @lockdep_map: user-defined lockdep_map
+ * @...: args for @fmt
+ *
+ * Same as alloc_workqueue but with the a user-defined lockdep_map. Useful for
+ * workqueues created with the same purpose and to avoid leaking a lockdep_map
+ * on each workqueue creation.
+ *
+ * RETURNS:
+ * Pointer to the allocated workqueue on success, %NULL on failure.
+ */
+__printf(1, 5) struct workqueue_struct *
+alloc_workqueue_lockdep_map(const char *fmt, unsigned int flags, int max_active,
+			    struct lockdep_map *lockdep_map, ...);
+
+#define alloc_ordered_workqueue_lockdep_map(fmt, flags, lockdep_map, args...)	\
+	alloc_workqueue_lockdep_map(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, lockdep_map, ##args)
+#endif
+
 /**
  * alloc_ordered_workqueue - allocate an ordered workqueue
  * @fmt: printf format for the name of the workqueue
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b3fa4d044f69..e1361dedbe06 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4795,11 +4795,17 @@ static void wq_init_lockdep(struct workqueue_struct *wq)
 
 static void wq_unregister_lockdep(struct workqueue_struct *wq)
 {
+	if (wq->flags & __WQ_USER_OWNED_LOCKDEP)
+		return;
+
 	lockdep_unregister_key(&wq->key);
 }
 
 static void wq_free_lockdep(struct workqueue_struct *wq)
 {
+	if (wq->flags & __WQ_USER_OWNED_LOCKDEP)
+		return;
+
 	if (wq->lock_name != wq->name)
 		kfree(wq->lock_name);
 }
@@ -5792,6 +5798,28 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 }
 EXPORT_SYMBOL_GPL(alloc_workqueue);
 
+#ifdef CONFIG_LOCKDEP
+__printf(1, 5)
+struct workqueue_struct *
+alloc_workqueue_lockdep_map(const char *fmt, unsigned int flags,
+			    int max_active, struct lockdep_map *lockdep_map, ...)
+{
+	struct workqueue_struct *wq;
+	va_list args;
+
+	va_start(args, lockdep_map);
+	wq = __alloc_workqueue(fmt, flags | __WQ_USER_OWNED_LOCKDEP, max_active, args);
+	va_end(args);
+	if (!wq)
+		return NULL;
+
+	wq->lockdep_map = lockdep_map;
+
+	return wq;
+}
+EXPORT_SYMBOL_GPL(alloc_workqueue_lockdep_map);
+#endif
+
 static bool pwq_busy(struct pool_workqueue *pwq)
 {
 	int i;
-- 
2.34.1