[PATCH v7 6/6] lib/dlock-list: Add an IRQ-safe mode to be used in interrupt handler

[Waiman Long]

To enable the use of dlock-list in an interrupt handler, a new
irqsafe mode can now be specified at dlock-list allocation time as
an additional argument to alloc_dlock_list_heads(). With that mode
specified, the spin_lock_irqsave/spin_unlock_irqrestore pair will be
used instead of the regular lock and unlock calls.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 fs/super.c                 |  2 +-
 include/linux/dlock-list.h | 18 +++++++++++++++---
 lib/dlock-list.c           | 44 +++++++++++++++++++++++++++++++-------------
 3 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index a90a070..0840e54 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -214,7 +214,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	INIT_LIST_HEAD(&s->s_inodes_wb);
 	spin_lock_init(&s->s_inode_wblist_lock);
 
-	if (alloc_dlock_list_heads(&s->s_inodes))
+	if (alloc_dlock_list_heads(&s->s_inodes, false))
 		goto fail;
 	if (list_lru_init_memcg(&s->s_dentry_lru))
 		goto fail;
diff --git a/include/linux/dlock-list.h b/include/linux/dlock-list.h
index 16474ae..2ba7b4f 100644
--- a/include/linux/dlock-list.h
+++ b/include/linux/dlock-list.h
@@ -32,6 +32,8 @@
 struct dlock_list_head {
 	struct list_head list;
 	spinlock_t lock;
+	int irqsafe;	/* IRQ safe mode */
+	unsigned long flags;
 } ____cacheline_aligned_in_smp;
 
 struct dlock_list_heads {
@@ -89,7 +91,12 @@ static inline void init_dlock_list_node(struct dlock_list_node *node)
  */
 static inline void dlock_list_unlock(struct dlock_list_iter *iter)
 {
-	spin_unlock(&iter->entry->lock);
+	struct dlock_list_head *h = iter->entry;
+
+	if (h->irqsafe)
+		spin_unlock_irqrestore(&h->lock, h->flags);
+	else
+		spin_unlock(&h->lock);
 }
 
 /**
@@ -98,13 +105,18 @@ static inline void dlock_list_unlock(struct dlock_list_iter *iter)
  */
 static inline void dlock_list_relock(struct dlock_list_iter *iter)
 {
-	spin_lock(&iter->entry->lock);
+	struct dlock_list_head *h = iter->entry;
+
+	if (h->irqsafe)
+		spin_lock_irqsave(&h->lock, h->flags);
+	else
+		spin_lock(&h->lock);
 }
 
 /*
  * Allocation and freeing of dlock list
  */
-extern int  alloc_dlock_list_heads(struct dlock_list_heads *dlist);
+extern int  alloc_dlock_list_heads(struct dlock_list_heads *dlist, int irqsafe);
 extern void free_dlock_list_heads(struct dlock_list_heads *dlist);
 
 /*
diff --git a/lib/dlock-list.c b/lib/dlock-list.c
index 8cd0876..4fded20 100644
--- a/lib/dlock-list.c
+++ b/lib/dlock-list.c
@@ -99,7 +99,8 @@ static int __init cpu2idx_init(void)
 
 /**
  * alloc_dlock_list_heads - Initialize and allocate the list of head entries
- * @dlist: Pointer to the dlock_list_heads structure to be initialized
+ * @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
  *
  * This function does not allocate the dlock_list_heads structure itself. The
@@ -112,7 +113,7 @@ static int __init cpu2idx_init(void)
  * The extra lists will not be ever used as all the cpu2idx entries will be
  * 0 before initialization.
  */
-int alloc_dlock_list_heads(struct dlock_list_heads *dlist)
+int alloc_dlock_list_heads(struct dlock_list_heads *dlist, int irqsafe)
 {
 	int idx, cnt = nr_dlock_lists ? nr_dlock_lists : nr_cpu_ids;
 
@@ -126,6 +127,7 @@ int alloc_dlock_list_heads(struct dlock_list_heads *dlist)
 
 		INIT_LIST_HEAD(&head->list);
 		head->lock = __SPIN_LOCK_UNLOCKED(&head->lock);
+		head->irqsafe = irqsafe;
 		lockdep_set_class(&head->lock, &dlock_list_key);
 	}
 	return 0;
@@ -194,13 +196,19 @@ struct dlock_list_head *dlock_list_hash(struct dlock_list_heads *dlist,
 void dlock_list_add(struct dlock_list_node *node,
 		    struct dlock_list_head *head)
 {
-	/*
-	 * There is no need to disable preemption
-	 */
-	spin_lock(&head->lock);
-	node->head = head;
-	list_add(&node->list, &head->list);
-	spin_unlock(&head->lock);
+	unsigned long flags;
+
+	if (head->irqsafe) {
+		spin_lock_irqsave(&head->lock, flags);
+		node->head = head;
+		list_add(&node->list, &head->list);
+		spin_unlock_irqrestore(&head->lock, flags);
+	} else {
+		spin_lock(&head->lock);
+		node->head = head;
+		list_add(&node->list, &head->list);
+		spin_unlock(&head->lock);
+	}
 }
 
 /**
@@ -232,6 +240,7 @@ void dlock_lists_add(struct dlock_list_node *node,
 void dlock_lists_del(struct dlock_list_node *node)
 {
 	struct dlock_list_head *head;
+	unsigned long flags;
 	bool retry;
 
 	do {
@@ -240,7 +249,11 @@ void dlock_lists_del(struct dlock_list_node *node)
 			      __func__, (unsigned long)node))
 			return;
 
-		spin_lock(&head->lock);
+		if (head->irqsafe)
+			spin_lock_irqsave(&head->lock, flags);
+		else
+			spin_lock(&head->lock);
+
 		if (likely(head == node->head)) {
 			list_del_init(&node->list);
 			node->head = NULL;
@@ -253,7 +266,11 @@ void dlock_lists_del(struct dlock_list_node *node)
 			 */
 			retry = (node->head != NULL);
 		}
-		spin_unlock(&head->lock);
+
+		if (head->irqsafe)
+			spin_unlock_irqrestore(&head->lock, flags);
+		else
+			spin_unlock(&head->lock);
 	} while (retry);
 }
 
@@ -272,7 +289,7 @@ struct dlock_list_node *__dlock_list_next_list(struct dlock_list_iter *iter)
 
 restart:
 	if (iter->entry) {
-		spin_unlock(&iter->entry->lock);
+		dlock_list_unlock(iter);
 		iter->entry = NULL;
 	}
 
@@ -287,7 +304,8 @@ struct dlock_list_node *__dlock_list_next_list(struct dlock_list_iter *iter)
 		goto next_list;
 
 	head = iter->entry = &iter->head[iter->index];
-	spin_lock(&head->lock);
+	dlock_list_relock(iter);
+
 	/*
 	 * There is a slight chance that the list may become empty just
 	 * before the lock is acquired. So an additional check is
-- 
1.8.3.1