fuse: Separate fuse device allocation and installation in fuse_conn

task #28910367
commit 0cd1eb9a4160a96e0ec9b93b2e7b489f449bf22d upstream

As of now fuse_dev_alloc() both allocates a fuse device and installs it
in fuse_conn list. fuse_dev_alloc() can fail if fuse_device allocation
fails.

virtio-fs needs to initialize multiple fuse devices (one per virtio
queue). It initializes one fuse device as part of call to
fuse_fill_super_common() and rest of the devices are allocated and
installed after that.

But, we can't affort to fail after calling fuse_fill_super_common() as
we don't have a way to undo all the actions done by fuse_fill_super_common().
So to avoid failures after the call to fuse_fill_super_common(),
pre-allocate all fuse devices early and install them into fuse connection
later.

This patch provides two separate helpers for fuse device allocation and
fuse device installation in fuse_conn.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NLiu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>

fs/fuse/cuse.c

@@ -505,7 +505,7 @@ static int cuse_channel_open(struct inode *inode, struct file *file)
 	 */
 	fuse_conn_init(&cc->fc, file->f_cred->user_ns, &fuse_dev_fiq_ops, NULL);
 
-	fud = fuse_dev_alloc(&cc->fc);
+	fud = fuse_dev_alloc_install(&cc->fc);
 	if (!fud) {
 		kfree(cc);
 		return -ENOMEM;

fs/fuse/dev.c

@@ -2283,7 +2283,7 @@ static int fuse_device_clone(struct fuse_conn *fc, struct file *new)
 	if (new->private_data)
 		return -EINVAL;
 
-	fud = fuse_dev_alloc(fc);
+	fud = fuse_dev_alloc_install(fc);
 	if (!fud)
 		return -ENOMEM;
 

fs/fuse/fuse_i.h

@@ -955,7 +955,9 @@ void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns,
  */
 void fuse_conn_put(struct fuse_conn *fc);
 
-struct fuse_dev *fuse_dev_alloc(struct fuse_conn *fc);
+struct fuse_dev *fuse_dev_alloc_install(struct fuse_conn *fc);
+struct fuse_dev *fuse_dev_alloc(void);
+void fuse_dev_install(struct fuse_dev *fud, struct fuse_conn *fc);
 void fuse_dev_free(struct fuse_dev *fud);
 
 /**

fs/fuse/inode.c

@@ -1012,24 +1012,40 @@ static int fuse_bdi_init(struct fuse_conn *fc, struct super_block *sb)
 	return 0;
 }
 
-struct fuse_dev *fuse_dev_alloc(struct fuse_conn *fc)
+struct fuse_dev *fuse_dev_alloc(void)
 {
 	struct fuse_dev *fud;
 
 	fud = kzalloc(sizeof(struct fuse_dev), GFP_KERNEL);
-	if (fud) {
-		fud->fc = fuse_conn_get(fc);
+	if (fud)
 		fuse_pqueue_init(&fud->pq);
 
-		spin_lock(&fc->lock);
-		list_add_tail(&fud->entry, &fc->devices);
-		spin_unlock(&fc->lock);
-	}
-
 	return fud;
 }
 EXPORT_SYMBOL_GPL(fuse_dev_alloc);
 
+void fuse_dev_install(struct fuse_dev *fud, struct fuse_conn *fc)
+{
+	fud->fc = fuse_conn_get(fc);
+	spin_lock(&fc->lock);
+	list_add_tail(&fud->entry, &fc->devices);
+	spin_unlock(&fc->lock);
+}
+EXPORT_SYMBOL_GPL(fuse_dev_install);
+
+struct fuse_dev *fuse_dev_alloc_install(struct fuse_conn *fc)
+{
+	struct fuse_dev *fud;
+
+	fud = fuse_dev_alloc();
+	if (!fud)
+		return NULL;
+
+	fuse_dev_install(fud, fc);
+	return fud;
+}
+EXPORT_SYMBOL_GPL(fuse_dev_alloc_install);
+
 void fuse_dev_free(struct fuse_dev *fud)
 {
 	struct fuse_conn *fc = fud->fc;
@@ -1099,7 +1115,7 @@ int fuse_fill_super_common(struct super_block *sb,
 	fuse_conn_init(fc, sb->s_user_ns, fiq_ops, fiq_priv);
 	fc->release = fuse_free_conn;
 
-	fud = fuse_dev_alloc(fc);
+	fud = fuse_dev_alloc_install(fc);
 	if (!fud)
 		goto err_put_conn;