Prior to this patchset, fuse_dev (containing fuse_pqueue) was allocated on
mount.  But now fuse_dev is allocated when opening /dev/fuse, even though
the queues are not needed at that time.

Delay allocation of the pqueue (4k worth of list_head) just before mounting
or cloning a device.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/fuse/dev.c       |  9 ++++++--
 fs/fuse/dev_uring.c |  2 +-
 fs/fuse/fuse_i.h    |  5 +++--
 fs/fuse/inode.c     | 51 +++++++++++++++++++++++++++++----------------
 fs/fuse/virtio_fs.c |  4 ++--
 5 files changed, 46 insertions(+), 25 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 3d6578fcb386..d18796b1010c 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1546,7 +1546,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 
 static int fuse_dev_open(struct inode *inode, struct file *file)
 {
-	struct fuse_dev *fud = fuse_dev_alloc();
+	struct fuse_dev *fud = fuse_dev_alloc(false);
 
 	if (!fud)
 		return -ENOMEM;
@@ -2580,6 +2580,7 @@ static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
 {
 	int oldfd;
 	struct fuse_dev *fud, *new_fud;
+	struct list_head *pq;
 
 	if (get_user(oldfd, argp))
 		return -EFAULT;
@@ -2599,8 +2600,12 @@ static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
 	if (!fud)
 		return -EINVAL;
 
+	pq = fuse_pqueue_alloc();
+	if (!pq)
+		return -ENOMEM;
+
 	new_fud = fuse_file_to_fud(file);
-	if (!fuse_dev_install(new_fud, fud->fc))
+	if (!fuse_dev_install(new_fud, fud->fc, pq))
 		return -EINVAL;
 
 	return 0;
diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index 7b9822e8837b..fb4f21c871fb 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -277,7 +277,7 @@ static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
 	queue = kzalloc_obj(*queue, GFP_KERNEL_ACCOUNT);
 	if (!queue)
 		return NULL;
-	pq = kzalloc_objs(struct list_head, FUSE_PQ_HASH_SIZE);
+	pq = fuse_pqueue_alloc();
 	if (!pq) {
 		kfree(queue);
 		return NULL;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 77f1c7cf24d2..e22d65e5ecff 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1340,8 +1340,9 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 void fuse_conn_put(struct fuse_conn *fc);
 
 struct fuse_dev *fuse_dev_alloc_install(struct fuse_conn *fc);
-struct fuse_dev *fuse_dev_alloc(void);
-bool fuse_dev_install(struct fuse_dev *fud, struct fuse_conn *fc);
+struct list_head *fuse_pqueue_alloc(void);
+struct fuse_dev *fuse_dev_alloc(bool alloc_pq);
+bool fuse_dev_install(struct fuse_dev *fud, struct fuse_conn *fc, struct list_head *pq);
 void fuse_dev_put(struct fuse_dev *fud);
 int fuse_send_init(struct fuse_mount *fm);
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 7065614d02c9..f388d57fdd8f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -977,15 +977,22 @@ static void fuse_iqueue_init(struct fuse_iqueue *fiq,
 
 void fuse_pqueue_init(struct fuse_pqueue *fpq)
 {
-	unsigned int i;
-
 	spin_lock_init(&fpq->lock);
-	for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
-		INIT_LIST_HEAD(&fpq->processing[i]);
 	INIT_LIST_HEAD(&fpq->io);
 	fpq->connected = 1;
 }
 
+struct list_head *fuse_pqueue_alloc(void)
+{
+	struct list_head *pq = kzalloc_objs(struct list_head, FUSE_PQ_HASH_SIZE);
+
+	if (pq) {
+		for (int i = 0; i < FUSE_PQ_HASH_SIZE; i++)
+			INIT_LIST_HEAD(&pq[i]);
+	}
+	return pq;
+}
+
 void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 		    struct user_namespace *user_ns,
 		    const struct fuse_iqueue_ops *fiq_ops, void *fiq_priv)
@@ -1633,33 +1640,38 @@ static int fuse_bdi_init(struct fuse_conn *fc, struct super_block *sb)
 	return 0;
 }
 
-struct fuse_dev *fuse_dev_alloc(void)
+struct fuse_dev *fuse_dev_alloc(bool alloc_pq)
 {
 	struct fuse_dev *fud;
-	struct list_head *pq;
+	struct list_head *pq __free(kfree) = NULL;
+
+	if (alloc_pq) {
+		pq = fuse_pqueue_alloc();
+		if (!pq)
+			return NULL;
+	}
 
 	fud = kzalloc_obj(struct fuse_dev);
 	if (!fud)
 		return NULL;
 
 	refcount_set(&fud->ref, 1);
-	pq = kzalloc_objs(struct list_head, FUSE_PQ_HASH_SIZE);
-	if (!pq) {
-		kfree(fud);
-		return NULL;
-	}
-
-	fud->pq.processing = pq;
+	fud->pq.processing = no_free_ptr(pq);
 	fuse_pqueue_init(&fud->pq);
 
 	return fud;
 }
 EXPORT_SYMBOL_GPL(fuse_dev_alloc);
 
-bool fuse_dev_install(struct fuse_dev *fud, struct fuse_conn *fc)
+bool fuse_dev_install(struct fuse_dev *fud, struct fuse_conn *fc, struct list_head *pq)
 {
 	struct fuse_conn *old_fc;
 
+	if (!pq)
+		WARN_ON(!fud->pq.processing);
+	else if (cmpxchg(&fud->pq.processing, NULL, pq))
+		kfree(pq);
+
 	fuse_conn_get(fc);
 	spin_lock(&fc->lock);
 	/*
@@ -1687,13 +1699,12 @@ EXPORT_SYMBOL_GPL(fuse_dev_install);
 
 struct fuse_dev *fuse_dev_alloc_install(struct fuse_conn *fc)
 {
-	struct fuse_dev *fud;
+	struct fuse_dev *fud = fuse_dev_alloc(true);
 
-	fud = fuse_dev_alloc();
 	if (!fud)
 		return NULL;
 
-	fuse_dev_install(fud, fc);
+	fuse_dev_install(fud, fc, NULL);
 	return fud;
 }
 EXPORT_SYMBOL_GPL(fuse_dev_alloc_install);
@@ -1871,10 +1882,14 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 	struct fuse_dev *fud = ctx->fud;
 	struct fuse_mount *fm = get_fuse_mount_super(sb);
 	struct fuse_conn *fc = fm->fc;
+	struct list_head *pq __free(kfree) = fuse_pqueue_alloc();
 	struct inode *root;
 	struct dentry *root_dentry;
 	int err;
 
+	if (!pq)
+		return -ENOMEM;
+
 	err = -EINVAL;
 	if (sb->s_flags & SB_MANDLOCK)
 		goto err;
@@ -1946,7 +1961,7 @@ 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;
 	if (fud) {
-		if (!fuse_dev_install(fud, fc))
+		if (!fuse_dev_install(fud, fc, no_free_ptr(pq)))
 			fc->connected = 0; /* device file got closed */
 		else
 			wake_up_all(&fuse_dev_waitq);
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 12300651a0f1..cc6426992ecd 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -1585,7 +1585,7 @@ static int virtio_fs_fill_super(struct super_block *sb, struct fs_context *fsc)
 	for (i = 0; i < fs->nvqs; i++) {
 		struct virtio_fs_vq *fsvq = &fs->vqs[i];
 
-		fsvq->fud = fuse_dev_alloc();
+		fsvq->fud = fuse_dev_alloc(true);
 		if (!fsvq->fud)
 			goto err_free_fuse_devs;
 	}
@@ -1606,7 +1606,7 @@ static int virtio_fs_fill_super(struct super_block *sb, struct fs_context *fsc)
 	for (i = 0; i < fs->nvqs; i++) {
 		struct virtio_fs_vq *fsvq = &fs->vqs[i];
 
-		fuse_dev_install(fsvq->fud, fc);
+		fuse_dev_install(fsvq->fud, fc, NULL);
 	}
 
 	/* Previous unmount will stop all queues. Start these again */
-- 
2.53.0