Re: [PATCH v2] fuse: Fix the condition to enable over-io-uring

[Baokun Li <libaokun@linux.alibaba.com>]

Hi Bernd,

On 2026/8/22 00:19, Bernd Schubert via B4 Relay wrote:
> + /* Once a connection has io-uring enabled on it, it can't be disabled */
> + if (!enable_uring && !fch->io_uring) {
> + pr_info_ratelimited("fuse-io-uring is disabled by module parameter\n");
> + return -EOPNOTSUPP;
> + }
> +
> + if (!fch->io_uring) {
> + pr_info_ratelimited(
> + "fuse-io-uring not enabled on this connection\n");
> + return -EOPNOTSUPP;
> + }

This combined with the REGISTER error path can hang IO when the ring is
already operational.  E.g. 100 entries, the 100th REGISTER fails after
ring->ready is set:

  new request:                        server fetch:
  fuse_send_one()                     IORING_OP_URING_CMD
    fiq->ops->send_req()                fuse_uring_cmd()
      fuse_uring_queue_fuse_req()         if (!fch->io_uring)  // == 0
        -> queued, no consumer              return -EOPNOTSUPP

The error path clears fch->io_uring but never reverts fiq->ops, so
requests keep flowing into io_uring queues while COMMIT_AND_FETCH is
rejected for all 99 active entries.

Maybe only tear down if the ring never became ready:

      if (err) {
          if (!fuse_uring_ready(fch)) {
              fch->io_uring = 0;
              wake_up_all(&fch->blocked_waitq);
              pr_info("[%u] fuse-io-uring disabled on connection err=%d\n",
                      fch->conn->dev, err);
          }
          return err;
      }


Regards,
Baokun