fuse: create fuse_dev on /dev/fuse open instead of mount

Allocate struct fuse_dev when opening the device.  This means that unlike
before, ->private_data is always set to a valid pointer.

The use of USE_DEV_SYNC_INIT magic pointer for the private_data is now
replaced with a simple bool sync_init member.

If sync INIT is not set, I/O on the device returns error before mount.
Keep this behavior by checking for the ->fc member.  If fud->fc is set, the
mount has succeeded.  Testing this used READ_ONCE(file->private_data) and
smp_mb() to try and provide the necessary semantics.  Switch this to
smp_store_release() and smp_load_acquire().

Setting fud->fc is protected by fuse_mutex, this is unchanged.

Will need this later so the /dev/fuse open file reference is not held
during FSCONFIG_CMD_CREATE.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

1 files changed, 18 insertions, 29 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 952dd56f0a02..0c03bbb21c12 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1548,32 +1548,24 @@ out_end:
 
 static int fuse_dev_open(struct inode *inode, struct file *file)
 {
-	/*
-	 * The fuse device's file's private_data is used to hold
-	 * the fuse_conn(ection) when it is mounted, and is used to
-	 * keep track of whether the file has been mounted already.
-	 */
-	file->private_data = NULL;
+	struct fuse_dev *fud = fuse_dev_alloc();
+
+	if (!fud)
+		return -ENOMEM;
+
+	file->private_data = fud;
 	return 0;
 }
 
 struct fuse_dev *fuse_get_dev(struct file *file)
 {
-	struct fuse_dev *fud = __fuse_get_dev(file);
+	struct fuse_dev *fud = fuse_file_to_fud(file);
 	int err;
 
-	if (likely(fud))
-		return fud;
-
-	err = wait_event_interruptible(fuse_dev_waitq,
-				       READ_ONCE(file->private_data) != FUSE_DEV_SYNC_INIT);
+	err = wait_event_interruptible(fuse_dev_waitq, fuse_dev_fc_get(fud) != NULL);
 	if (err)
 		return ERR_PTR(err);
 
-	fud = __fuse_get_dev(file);
-	if (!fud)
-		return ERR_PTR(-EPERM);
-
 	return fud;
 }
 
@@ -2547,10 +2539,10 @@ void fuse_wait_aborted(struct fuse_conn *fc)
 
 int fuse_dev_release(struct inode *inode, struct file *file)
 {
-	struct fuse_dev *fud = __fuse_get_dev(file);
+	struct fuse_dev *fud = fuse_file_to_fud(file);
+	struct fuse_conn *fc = fuse_dev_fc_get(fud);
 
-	if (fud) {
-		struct fuse_conn *fc = fud->fc;
+	if (fc) {
 		struct fuse_pqueue *fpq = &fud->pq;
 		LIST_HEAD(to_end);
 		unsigned int i;
@@ -2568,8 +2560,8 @@ int fuse_dev_release(struct inode *inode, struct file *file)
 			WARN_ON(fc->iq.fasync != NULL);
 			fuse_abort_conn(fc);
 		}
-		fuse_dev_free(fud);
 	}
+	fuse_dev_free(fud);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(fuse_dev_release);
@@ -2587,16 +2579,12 @@ static int fuse_dev_fasync(int fd, struct file *file, int on)
 
 static int fuse_device_clone(struct fuse_conn *fc, struct file *new)
 {
-	struct fuse_dev *fud;
+	struct fuse_dev *new_fud = fuse_file_to_fud(new);
 
-	if (__fuse_get_dev(new))
+	if (fuse_dev_fc_get(new_fud))
 		return -EINVAL;
 
-	fud = fuse_dev_alloc_install(fc);
-	if (!fud)
-		return -ENOMEM;
-
-	new->private_data = fud;
+	fuse_dev_install(new_fud, fc);
 	atomic_inc(&fc->dev_count);
 
 	return 0;
@@ -2667,10 +2655,11 @@ static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
 static long fuse_dev_ioctl_sync_init(struct file *file)
 {
 	int err = -EINVAL;
+	struct fuse_dev *fud = fuse_file_to_fud(file);
 
 	mutex_lock(&fuse_mutex);
-	if (!__fuse_get_dev(file)) {
-		WRITE_ONCE(file->private_data, FUSE_DEV_SYNC_INIT);
+	if (!fuse_dev_fc_get(fud)) {
+		fud->sync_init = true;
 		err = 0;
 	}
 	mutex_unlock(&fuse_mutex);