Re: [PATCH v6 1/6] fuse: decouple fuse_ring creation from ent registration

On 7/16/26 19:59, Joanne Koong wrote:
> Currently, the connection's fuse_ring is created lazily on the first
> FUSE_IO_URING_CMD_REGISTER command. A server registers entries from one
> thread per queue (one per CPU) and those threads issue their first
> REGISTER command concurrently. They then race to create the single
> per-connection fuse_ring, which required open-coded handling in
> fuse_uring_create() to detect and protect against concurrent creations.
> 
> Decouple fuse_ring creation from ent registration and move it to
> FUSE_INIT reply processing after a server has negotiated and set
> FUSE_OVER_IO_URING. The ring is published before the connection is
> marked initialized. fuse_uring_register() no longer creates the ring and
> it instead uses the ring set up at init time.
> 
> Signed-off-by: Joanne Koong <[email protected]>
> ---
>  fs/fuse/dev.c         |  8 +++-----
>  fs/fuse/dev.h         |  2 +-
>  fs/fuse/dev_uring.c   | 26 ++++++++++----------------
>  fs/fuse/dev_uring_i.h |  5 +++++
>  fs/fuse/inode.c       |  4 +++-
>  5 files changed, 22 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 8b68b24af9d7..d50792162d8b 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -75,6 +75,9 @@ void fuse_chan_set_initialized(struct fuse_chan *fch, struct fuse_chan_param *pa
>  		fch->minor = param->minor;
>  		fch->max_write = param->max_write;
>  		fch->max_pages = param->max_pages;
> +
> +		if (param->io_uring_enabled)
> +			fuse_uring_conn_init(fch);
>  	}
>  
>  	/* Pairs with smp_load_acquire() readers of fch->initialized */
> @@ -411,11 +414,6 @@ void fuse_chan_set_fc(struct fuse_chan *fch, struct fuse_conn *fc)
>  	fch->conn = fc;
>  }
>  
> -void fuse_chan_io_uring_enable(struct fuse_chan *fch)
> -{
> -	fch->io_uring = 1;
> -}
> -
>  void fuse_pqueue_init(struct fuse_pqueue *fpq)
>  {
>  	spin_lock_init(&fpq->lock);
> diff --git a/fs/fuse/dev.h b/fs/fuse/dev.h
> index aed69fd14c41..8d25378c0918 100644
> --- a/fs/fuse/dev.h
> +++ b/fs/fuse/dev.h
> @@ -22,6 +22,7 @@ struct fuse_chan_param {
>  	unsigned int minor;
>  	unsigned int max_write;
>  	unsigned int max_pages;
> +	bool io_uring_enabled;
>  };
>  
>  struct fuse_chan *fuse_chan_new(void);
> @@ -34,7 +35,6 @@ void fuse_chan_max_background_set(struct fuse_chan *fch, unsigned int val);
>  unsigned int fuse_chan_num_waiting(struct fuse_chan *fch);
>  void fuse_chan_set_fc(struct fuse_chan *fch, struct fuse_conn *fc);
>  void fuse_chan_set_initialized(struct fuse_chan *fch, struct fuse_chan_param *param);
> -void fuse_chan_io_uring_enable(struct fuse_chan *fch);
>  ssize_t fuse_chan_send(struct fuse_chan *fch, struct fuse_args *args);
>  int fuse_chan_send_bg(struct fuse_chan *fch, struct fuse_args *args, gfp_t gfp_flags);
>  int fuse_chan_send_notify_reply(struct fuse_chan *fch, struct fuse_args *args, u64 unique);
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index bf9d51f2a508..b7c6100c4176 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -238,7 +238,6 @@ static struct fuse_ring *fuse_uring_create(struct fuse_chan *fch)
>  {
>  	struct fuse_ring *ring;
>  	size_t nr_queues = num_possible_cpus();
> -	struct fuse_ring *res = NULL;
>  	size_t max_payload_size;
>  
>  	ring = kzalloc_obj(*ring, GFP_KERNEL_ACCOUNT);
> @@ -258,12 +257,6 @@ static struct fuse_ring *fuse_uring_create(struct fuse_chan *fch)
>  		spin_unlock(&fch->lock);
>  		goto out_err;
>  	}
> -	if (fch->ring) {
> -		/* race, another thread created the ring in the meantime */
> -		spin_unlock(&fch->lock);
> -		res = fch->ring;
> -		goto out_err;
> -	}
>  
>  	init_waitqueue_head(&ring->stop_waitq);
>  
> @@ -278,7 +271,13 @@ static struct fuse_ring *fuse_uring_create(struct fuse_chan *fch)
>  out_err:
>  	kfree(ring->queues);
>  	kfree(ring);
> -	return res;
> +	return NULL;
> +}
> +
> +void fuse_uring_conn_init(struct fuse_chan *fch)
> +{
> +	if (fuse_uring_create(fch))
> +		fch->io_uring = 1;
>  }
>  
>  static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
> @@ -1178,15 +1177,10 @@ static int fuse_uring_register(struct io_uring_cmd *cmd,
>  	struct fuse_ring *ring = smp_load_acquire(&fch->ring);
>  	struct fuse_ring_queue *queue;
>  	struct fuse_ring_ent *ent;
> -	int err;
>  	unsigned int qid = READ_ONCE(cmd_req->qid);
>  
> -	err = -ENOMEM;
> -	if (!ring) {
> -		ring = fuse_uring_create(fch);
> -		if (!ring)
> -			return err;
> -	}
> +	if (!ring)
> +		return -EINVAL;
>  
>  	if (qid >= ring->nr_queues) {
>  		pr_info_ratelimited("fuse: Invalid ring qid %u\n", qid);
> @@ -1197,7 +1191,7 @@ static int fuse_uring_register(struct io_uring_cmd *cmd,
>  	if (!queue) {
>  		queue = fuse_uring_create_queue(ring, qid);
>  		if (!queue)
> -			return err;
> +			return -ENOMEM;
>  	}
>  
>  	/*
> diff --git a/fs/fuse/dev_uring_i.h b/fs/fuse/dev_uring_i.h
> index 55f8d04e4b0b..d721a4fc0215 100644
> --- a/fs/fuse/dev_uring_i.h
> +++ b/fs/fuse/dev_uring_i.h
> @@ -135,6 +135,7 @@ struct fuse_ring {
>  	bool ready;
>  };
>  
> +void fuse_uring_conn_init(struct fuse_chan *fch);
>  void fuse_uring_stop_queues(struct fuse_ring *ring);
>  void fuse_uring_abort_end_requests(struct fuse_ring *ring);
>  int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags);
> @@ -174,6 +175,10 @@ static inline bool fuse_uring_ready(struct fuse_chan *fch)
>  
>  #else /* CONFIG_FUSE_IO_URING */
>  
> +static inline void fuse_uring_conn_init(struct fuse_chan *fch)
> +{
> +}
> +
>  static inline void fuse_uring_abort(struct fuse_chan *fch)
>  {
>  }
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index d975073c6029..ce4891a04a37 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1272,6 +1272,7 @@ static void process_init_reply(struct fuse_args *args, int error)
>  	struct fuse_mount *fm = ia->fm;
>  	struct fuse_conn *fc = fm->fc;
>  	struct fuse_init_out *arg = &ia->out;
> +	bool io_uring_enabled = false;
>  	bool ok = true;
>  
>  	if (error || arg->major != FUSE_KERNEL_VERSION)
> @@ -1402,7 +1403,7 @@ static void process_init_reply(struct fuse_args *args, int error)
>  					ok = false;
>  			}
>  			if (flags & FUSE_OVER_IO_URING && fuse_uring_enabled())
> -				fuse_chan_io_uring_enable(fc->chan);
> +				io_uring_enabled = true;
>  
>  			if (flags & FUSE_REQUEST_TIMEOUT)
>  				timeout = arg->request_timeout;
> @@ -1432,6 +1433,7 @@ static void process_init_reply(struct fuse_args *args, int error)
>  			.minor = fc->minor,
>  			.max_write = fc->max_write,
>  			.max_pages = fc->max_pages,
> +			.io_uring_enabled = io_uring_enabled,
>  		};
>  		fuse_chan_set_initialized(fc->chan, &cp);
>  	}

Thanks, I should have done that from the beginning!

Reviewed-by: Bernd Schubert <[email protected]>