From: Vivek Goyal <vgoyal@redhat.com>
Date: Mon, 4 May 2020 14:33:15 -0400
Subject: virtiofs: do not use fuse_fill_super_common() for device installation
Git-commit: 7fd3abfa8dd7c08ecacd25b2f9f9e1d3fb642440
Patch-mainline: v5.8-rc1
References: jsc#SLE-13782

fuse_fill_super_common() allocates and installs one fuse_device.  Hence
virtiofs allocates and install all fuse devices by itself except one.

This makes logic little twisted.  There does not seem to be any real need
that why virtiofs can't allocate and install all fuse devices itself.

So opt out of fuse device allocation and installation while calling
fuse_fill_super_common().

Regular fuse still wants fuse_fill_super_common() to install fuse_device.
It needs to prevent against races where two mounters are trying to mount
fuse using same fd.  In that case one will succeed while other will get
-EINVAL.

virtiofs does not have this issue because sget_fc() resolves the race
w.r.t multiple mounters and only one instance of virtio_fs_fill_super()
should be in progress for same filesystem.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Acked-by: Luis Henriques <lhenriques@suse.com>
---
 fs/fuse/inode.c     | 19 ++++++++++++-------
 fs/fuse/virtio_fs.c |  9 +++------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 95d712d44ca1..6fae66cc096a 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1113,7 +1113,7 @@ EXPORT_SYMBOL_GPL(fuse_dev_free);
 
 int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 {
-	struct fuse_dev *fud;
+	struct fuse_dev *fud = NULL;
 	struct fuse_conn *fc = get_fuse_conn_super(sb);
 	struct inode *root;
 	struct dentry *root_dentry;
@@ -1155,9 +1155,12 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 	if (sb->s_user_ns != &init_user_ns)
 		sb->s_xattr = fuse_no_acl_xattr_handlers;
 
-	fud = fuse_dev_alloc_install(fc);
-	if (!fud)
-		goto err;
+	if (ctx->fudptr) {
+		err = -ENOMEM;
+		fud = fuse_dev_alloc_install(fc);
+		if (!fud)
+			goto err;
+	}
 
 	fc->dev = sb->s_dev;
 	fc->sb = sb;
@@ -1191,7 +1194,7 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 
 	mutex_lock(&fuse_mutex);
 	err = -EINVAL;
-	if (*ctx->fudptr)
+	if (ctx->fudptr && *ctx->fudptr)
 		goto err_unlock;
 
 	err = fuse_ctl_add_conn(fc);
@@ -1200,7 +1203,8 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 
 	list_add_tail(&fc->entry, &fuse_conn_list);
 	sb->s_root = root_dentry;
-	*ctx->fudptr = fud;
+	if (ctx->fudptr)
+		*ctx->fudptr = fud;
 	mutex_unlock(&fuse_mutex);
 	return 0;
 
@@ -1208,7 +1212,8 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 	mutex_unlock(&fuse_mutex);
 	dput(root_dentry);
  err_dev_free:
-	fuse_dev_free(fud);
+	if (fud)
+		fuse_dev_free(fud);
  err:
 	return err;
 }
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 0c6ef5d3c6ab..4c4ef5d69298 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -1103,7 +1103,7 @@ static int virtio_fs_fill_super(struct super_block *sb)
 
 	err = -ENOMEM;
 	/* Allocate fuse_dev for hiprio and notification queues */
-	for (i = 0; i < VQ_REQUEST; i++) {
+	for (i = 0; i < fs->nvqs; i++) {
 		struct virtio_fs_vq *fsvq = &fs->vqs[i];
 
 		fsvq->fud = fuse_dev_alloc();
@@ -1111,18 +1111,15 @@ static int virtio_fs_fill_super(struct super_block *sb)
 			goto err_free_fuse_devs;
 	}
 
-	ctx.fudptr = (void **)&fs->vqs[VQ_REQUEST].fud;
+	/* virtiofs allocates and installs its own fuse devices */
+	ctx.fudptr = NULL;
 	err = fuse_fill_super_common(sb, &ctx);
 	if (err < 0)
 		goto err_free_fuse_devs;
 
-	fc = fs->vqs[VQ_REQUEST].fud->fc;
-
 	for (i = 0; i < fs->nvqs; i++) {
 		struct virtio_fs_vq *fsvq = &fs->vqs[i];
 
-		if (i == VQ_REQUEST)
-			continue; /* already initialized */
 		fuse_dev_install(fsvq->fud, fc);
 	}