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: Vivek Goyal <vgo...@redhat.com>
---
 fs/fuse/cuse.c   |  2 +-
 fs/fuse/dev.c    |  2 +-
 fs/fuse/fuse_i.h |  4 +++-
 fs/fuse/inode.c  | 25 ++++++++++++++++++++-----
 4 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index a6ed7a036b50..a509747153a7 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -506,7 +506,7 @@ 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;
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ef489beadf58..ee9dd38bc0f0 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2318,7 +2318,7 @@ 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;
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 0b578e07156d..4008ed65a48d 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1050,7 +1050,9 @@ 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);
 void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req);
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 126e77854dac..9b0114437a14 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1027,8 +1027,7 @@ 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;
        struct list_head *pq;
 
@@ -1043,16 +1042,32 @@ struct fuse_dev *fuse_dev_alloc(struct fuse_conn *fc)
        }
 
        fud->pq.processing = pq;
-       fud->fc = fuse_conn_get(fc);
        fuse_pqueue_init(&fud->pq);
 
+       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);
+EXPORT_SYMBOL_GPL(fuse_dev_alloc_install);
 
 void fuse_dev_free(struct fuse_dev *fud)
 {
@@ -1122,7 +1137,7 @@ int fuse_fill_super_common(struct super_block *sb,
                       mount_data->fiq_priv);
        fc->release = fuse_free_conn;
 
-       fud = fuse_dev_alloc(fc);
+       fud = fuse_dev_alloc_install(fc);
        if (!fud)
                goto err_put_conn;
 
-- 
2.20.1

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