1 files changed, 32 insertions, 2 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 73ffa32e58ee..dfce80869145 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -322,13 +322,33 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
 }
 
 /**
+ * inode_to_wb_is_valid - test whether an inode has a wb associated
+ * @inode: inode of interest
+ *
+ * Returns %true if @inode has a wb associated.  May be called without any
+ * locking.
+ */
+static inline bool inode_to_wb_is_valid(struct inode *inode)
+{
+	return inode->i_wb;
+}
+
+/**
  * inode_to_wb - determine the wb of an inode
  * @inode: inode of interest
  *
- * Returns the wb @inode is currently associated with.
+ * Returns the wb @inode is currently associated with.  The caller must be
+ * holding either @inode->i_lock, @inode->i_mapping->tree_lock, or the
+ * associated wb's list_lock.
  */
 static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
 {
+#ifdef CONFIG_LOCKDEP
+	WARN_ON_ONCE(debug_locks &&
+		     (!lockdep_is_held(&inode->i_lock) &&
+		      !lockdep_is_held(&inode->i_mapping->tree_lock) &&
+		      !lockdep_is_held(&inode->i_wb->list_lock)));
+#endif
 	return inode->i_wb;
 }
 
@@ -360,7 +380,12 @@ unlocked_inode_to_wb_begin(struct inode *inode, bool *lockedp)
 
 	if (unlikely(*lockedp))
 		spin_lock_irq(&inode->i_mapping->tree_lock);
-	return inode_to_wb(inode);
+
+	/*
+	 * Protected by either !I_WB_SWITCH + rcu_read_lock() or tree_lock.
+	 * inode_to_wb() will bark.  Deref directly.
+	 */
+	return inode->i_wb;
 }
 
 /**
@@ -459,6 +484,11 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
 	return &bdi->wb;
 }
 
+static inline bool inode_to_wb_is_valid(struct inode *inode)
+{
+	return true;
+}
+
 static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
 {
 	return &inode_to_bdi(inode)->wb;