vfs: Take I_SYNC whilst performing fsync() and similar

fs/fs-writeback.c

@@ -2759,3 +2759,37 @@ int sync_inode_metadata(struct inode *inode, int wait)
 	return writeback_single_inode(inode, &wbc);
 }
 EXPORT_SYMBOL(sync_inode_metadata);
+
+/**
+ * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range
+ * @mapping:	address space structure to write
+ * @wbc:	the writeback_control controlling the writeout
+ *
+ * Call writepages on the mapping using the provided wbc to control the
+ * writeout.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int filemap_fdatawrite_wbc(struct address_space *mapping,
+			   struct writeback_control *wbc)
+{
+	struct inode *inode = mapping->host;
+	int ret;
+
+	if (!mapping_can_writeback(mapping) ||
+	    !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
+		return 0;
+
+	spin_lock(&inode->i_lock);
+	if (inode->i_state & I_SYNC) {
+		__inode_wait_for_writeback(inode);
+		WARN_ON(inode->i_state & I_SYNC);
+	}
+
+	wbc_attach_unlock_fdatawrite_inode(wbc, inode);
+	ret = do_writepages(mapping, wbc);
+	wbc_detach_inode(wbc);
+	inode_sync_complete(inode);
+	return ret;
+}
+EXPORT_SYMBOL(filemap_fdatawrite_wbc);

include/linux/writeback.h

@@ -267,6 +267,22 @@ static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
 	wbc_attach_and_unlock_inode(wbc, inode);
 }
 
+/**
+ * wbc_attach_unlock_fdatawrite_inode - associate wbc and inode for fdatawrite
+ * @wbc: writeback_control of interest
+ * @inode: target inode
+ *
+ * This function is to be used by __filemap_fdatawrite_range(), which is an
+ * alternative entry point into writeback code, and first ensures @inode is
+ * associated with a bdi_writeback and attaches it to @wbc.
+ */
+static inline void wbc_attach_unlock_fdatawrite_inode(struct writeback_control *wbc,
+						      struct inode *inode)
+{
+	inode_attach_wb(inode, NULL);
+	wbc_attach_and_unlock_inode(wbc, inode);
+}
+
 /**
  * wbc_init_bio - writeback specific initializtion of bio
  * @wbc: writeback_control for the writeback in progress

mm/filemap.c

@@ -361,32 +361,6 @@ static int filemap_check_and_keep_errors(struct address_space *mapping)
 	return 0;
 }
 
-/**
- * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range
- * @mapping:	address space structure to write
- * @wbc:	the writeback_control controlling the writeout
- *
- * Call writepages on the mapping using the provided wbc to control the
- * writeout.
- *
- * Return: %0 on success, negative error code otherwise.
- */
-int filemap_fdatawrite_wbc(struct address_space *mapping,
-			   struct writeback_control *wbc)
-{
-	int ret;
-
-	if (!mapping_can_writeback(mapping) ||
-	    !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
-		return 0;
-
-	wbc_attach_fdatawrite_inode(wbc, mapping->host);
-	ret = do_writepages(mapping, wbc);
-	wbc_detach_inode(wbc);
-	return ret;
-}
-EXPORT_SYMBOL(filemap_fdatawrite_wbc);
-
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:	address space structure to write