diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index b312a04f672b..457adfca5931 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -210,14 +210,78 @@ static void cachefiles_update_object(struct fscache_object *_object)
 	_leave("");
 }
 
+/*
+ * Shorten the backing object to discard any dirty data and free up
+ * any unused granules.
+ */
+static bool cachefiles_shorten_object(struct cachefiles_object *object, loff_t new_size)
+{
+	struct cachefiles_cache *cache;
+	struct inode *inode;
+	struct path path;
+	loff_t i_size;
+
+	cache = container_of(object->fscache.cache,
+			     struct cachefiles_cache, cache);
+	path.mnt = cache->mnt;
+	path.dentry = object->dentry;
+
+	inode = d_inode(object->dentry);
+	trace_cachefiles_trunc(object, inode, i_size_read(inode), new_size);
+	if (vfs_truncate(&path, new_size) < 0) {
+		cachefiles_io_error_obj(object, "Trunc-to-size failed");
+		cachefiles_remove_object_xattr(cache, object->dentry);
+		return false;
+	}
+
+	new_size = round_up(new_size, CACHEFILES_DIO_BLOCK_SIZE);
+	i_size = i_size_read(inode);
+	if (i_size < new_size) {
+		trace_cachefiles_trunc(object, inode, i_size, new_size);
+		if (vfs_truncate(&path, new_size) < 0) {
+			cachefiles_io_error_obj(object, "Trunc-to-dio-size failed");
+			cachefiles_remove_object_xattr(cache, object->dentry);
+			return false;
+		}
+	}
+
+	return true;
+}
+
+/*
+ * Trim excess stored data off of an object.
+ */
+static bool cachefiles_trim_object(struct cachefiles_object *object)
+{
+	loff_t object_size;
+
+	_enter("{OBJ%x}", object->fscache.debug_id);
+
+	object_size = object->fscache.cookie->object_size;
+	if (i_size_read(d_inode(object->dentry)) <= object_size)
+		return true;
+
+	return cachefiles_shorten_object(object, object_size);
+}
+
 /*
  * Commit changes to the object as we drop it.
  */
 static bool cachefiles_commit_object(struct cachefiles_object *object,
 				     struct cachefiles_cache *cache)
 {
+	bool update = false;
+
 	if (object->content_map_changed)
 		cachefiles_save_content_map(object);
+	if (test_and_clear_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->fscache.flags))
+		update = true;
+	if (test_and_clear_bit(FSCACHE_OBJECT_NEEDS_UPDATE, &object->fscache.flags))
+		update = true;
+	if (update) {
+		if (cachefiles_trim_object(object))
+			cachefiles_set_object_xattr(object);
+	}
 
 	if (test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags))
 		return cachefiles_commit_tmpfile(cache, object);
@@ -577,5 +641,6 @@ const struct fscache_cache_ops cachefiles_cache_ops = {
 	.shape_extent		= cachefiles_shape_extent,
 	.read			= cachefiles_read,
 	.write			= cachefiles_write,
+	.prepare_to_write	= cachefiles_prepare_to_write,
 	.display_object		= cachefiles_display_object,
 };
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index ccc8cd2b8250..487a434ddb75 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -248,7 +248,7 @@ extern int cachefiles_set_object_xattr(struct cachefiles_object *object);
 extern int cachefiles_check_auxdata(struct cachefiles_object *object);
 extern int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
 					  struct dentry *dentry);
-
+extern int cachefiles_prepare_to_write(struct fscache_object *object);
 
 /*
  * error handling
diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
index 22c56ca2fd0b..456301b7abb0 100644
--- a/fs/cachefiles/xattr.c
+++ b/fs/cachefiles/xattr.c
@@ -124,6 +124,8 @@ int cachefiles_set_object_xattr(struct cachefiles_object *object)
 	buf->zero_point		= cpu_to_be64(object->fscache.cookie->zero_point);
 	buf->type		= object->fscache.cookie->type;
 	buf->content		= object->content_info;
+	if (test_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->fscache.flags))
+		buf->content	= CACHEFILES_CONTENT_DIRTY;
 	if (len > 0)
 		memcpy(buf->data, fscache_get_aux(object->fscache.cookie), len);
 
@@ -184,10 +186,16 @@ int cachefiles_check_auxdata(struct cachefiles_object *object)
 		why = cachefiles_coherency_check_aux;
 	} else if (be64_to_cpu(buf->object_size) != object->fscache.cookie->object_size) {
 		why = cachefiles_coherency_check_objsize;
+	} else if (buf->content == CACHEFILES_CONTENT_DIRTY) {
+		// TODO: Begin conflict resolution
+		pr_warn("Dirty object in cache\n");
+		why = cachefiles_coherency_check_dirty;
 	} else {
 		object->fscache.cookie->zero_point = be64_to_cpu(buf->zero_point);
 		object->content_info = buf->content;
 		why = cachefiles_coherency_check_ok;
+		object->fscache.cookie->zero_point = be64_to_cpu(buf->zero_point);
+		object->content_info = buf->content;
 		ret = 0;
 	}
 
@@ -219,3 +227,16 @@ int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
 	_leave(" = %d", ret);
 	return ret;
 }
+
+/*
+ * Stick a marker on the cache object to indicate that it's dirty.
+ */
+int cachefiles_prepare_to_write(struct fscache_object *_object)
+{
+	struct cachefiles_object *object =
+		container_of(_object, struct cachefiles_object, fscache);
+
+	_enter("c=%08x", object->fscache.cookie->debug_id);
+
+	return cachefiles_set_object_xattr(object);
+}
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index c0d93dc7f69f..c96cd23bcdb2 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -342,6 +342,8 @@ EXPORT_SYMBOL(__fscache_acquire_cookie);
 void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
 {
 	enum fscache_cookie_stage stage;
+	struct fscache_object *object;
+	bool write_set;
 
 	_enter("c=%08x", cookie->debug_id);
 
@@ -360,7 +362,7 @@ void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
 
 		/* The lookup job holds its own active increment */
 		atomic_inc(&cookie->n_active);
-		fscache_dispatch(cookie, NULL, 0, fscache_lookup_object);
+		fscache_dispatch(cookie, NULL, will_modify, fscache_lookup_object);
 		break;
 
 	case FSCACHE_COOKIE_STAGE_INITIALISING:
@@ -373,8 +375,17 @@ void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
 	case FSCACHE_COOKIE_STAGE_NO_DATA_YET:
 	case FSCACHE_COOKIE_STAGE_ACTIVE:
 	case FSCACHE_COOKIE_STAGE_INVALIDATING:
-		// TODO: Handle will_modify
-		spin_unlock(&cookie->lock);
+		if (will_modify) {
+			object = hlist_entry(cookie->backing_objects.first,
+					     struct fscache_object, cookie_link);
+			write_set = test_and_set_bit(FSCACHE_OBJECT_LOCAL_WRITE,
+						     &object->flags);
+			spin_unlock(&cookie->lock);
+			if (!write_set)
+				fscache_dispatch(cookie, object, 0, fscache_prepare_to_write);
+		} else {
+			spin_unlock(&cookie->lock);
+		}
 		break;
 
 	case FSCACHE_COOKIE_STAGE_DEAD:
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index b9cad60e3c4e..0b370d059bdf 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -134,6 +134,7 @@ extern void fscache_lookup_object(struct fscache_cookie *, struct fscache_object
 extern void fscache_invalidate_object(struct fscache_cookie *, struct fscache_object *, int);
 extern void fscache_drop_object(struct fscache_cookie *, struct fscache_object *, bool);
 extern void fscache_discard_objects(struct fscache_cookie *, struct fscache_object *, int);
+extern void fscache_prepare_to_write(struct fscache_cookie *, struct fscache_object *, int);
 
 /*
  * object-list.c
diff --git a/fs/fscache/obj.c b/fs/fscache/obj.c
index aea4239641a9..332ba132413d 100644
--- a/fs/fscache/obj.c
+++ b/fs/fscache/obj.c
@@ -117,7 +117,8 @@ static bool fscache_wrangle_object(struct fscache_cookie *cookie,
  * Create an object chain, making sure that the index chain is fully created.
  */
 static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie *cookie,
-							  struct fscache_cache *cache)
+							  struct fscache_cache *cache,
+							  bool will_modify)
 {
 	struct fscache_object *object = NULL, *parent, *xobject;
 
@@ -131,7 +132,7 @@ static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie
 	spin_unlock(&cookie->lock);
 
 	/* Recurse to look up/create the parent index. */
-	parent = fscache_lookup_object_chain(cookie->parent, cache);
+	parent = fscache_lookup_object_chain(cookie->parent, cache, false);
 	if (IS_ERR(parent))
 		goto error;
 
@@ -146,9 +147,13 @@ static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie
 	if (!object)
 		goto error;
 
+	if (will_modify)
+		__set_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->flags);
+
 	xobject = fscache_attach_object(cookie, object);
 	if (xobject != object) {
 		fscache_do_put_object(object, fscache_obj_put_alloc_dup);
+		object = xobject;
 		goto object_exists;
 	}
 
@@ -199,7 +204,8 @@ static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie
  * - this must make sure the index chain is instantiated and instantiate the
  *   object representation too
  */
-static void fscache_lookup_object_locked(struct fscache_cookie *cookie)
+static void fscache_lookup_object_locked(struct fscache_cookie *cookie,
+					 bool will_modify)
 {
 	struct fscache_object *object;
 	struct fscache_cache *cache;
@@ -217,12 +223,16 @@ static void fscache_lookup_object_locked(struct fscache_cookie *cookie)
 
 	_debug("cache %s", cache->tag->name);
 
-	object = fscache_lookup_object_chain(cookie, cache);
+	object = fscache_lookup_object_chain(cookie, cache, will_modify);
 	if (!object) {
 		_leave(" [fail]");
 		return;
 	}
 
+	if (will_modify &&
+	    test_and_set_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->flags))
+		fscache_prepare_to_write(cookie, object, 0);
+
 	fscache_do_put_object(object, fscache_obj_put);
 	_leave(" [done]");
 }
@@ -231,7 +241,7 @@ void fscache_lookup_object(struct fscache_cookie *cookie,
 			   struct fscache_object *object, int param)
 {
 	down_read(&fscache_addremove_sem);
-	fscache_lookup_object_locked(cookie);
+	fscache_lookup_object_locked(cookie, param);
 	up_read(&fscache_addremove_sem);
 	__fscache_unuse_cookie(cookie, NULL, NULL);
 }
@@ -336,3 +346,12 @@ void fscache_discard_objects(struct fscache_cookie *cookie,
 	up_read(&fscache_addremove_sem);
 	_leave("");
 }
+
+/*
+ * Prepare a cache object to be written to.
+ */
+void fscache_prepare_to_write(struct fscache_cookie *cookie,
+			      struct fscache_object *object, int param)
+{
+	object->cache->ops->prepare_to_write(object);
+}
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 4fb63d8a60cd..848ced13c4ae 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -155,6 +155,9 @@ struct fscache_cache_ops {
 		     struct fscache_io_request *req,
 		     struct iov_iter *iter);
 
+	/* Prepare to write to a live cache object */
+	int (*prepare_to_write)(struct fscache_object *object);
+
 	/* Display object info in /proc/fs/fscache/objects */
 	int (*display_object)(struct seq_file *m, struct fscache_object *object);
 };
@@ -183,6 +186,7 @@ struct fscache_object {
 	spinlock_t		lock;		/* state and operations lock */
 
 	unsigned long		flags;
+#define FSCACHE_OBJECT_LOCAL_WRITE	1	/* T if the object is being modified locally */
 #define FSCACHE_OBJECT_NEEDS_INVAL	8	/* T if object needs invalidation */
 #define FSCACHE_OBJECT_NEEDS_UPDATE	9	/* T if object attrs need writing to disk */
 
