io_uring/register: limit ring resizing to DEFER_TASKRUN

JIRA: https://issues.redhat.com/browse/RHEL-106845

commit c261e4f
Author: Jens Axboe <[email protected]>
Date:   Thu Dec 19 09:32:26 2024 -0700

    io_uring/register: limit ring resizing to DEFER_TASKRUN

    With DEFER_TASKRUN, we know the ring can't be both waited upon and
    resized at the same time. This is important for CQ resizing. Allowing SQ
    ring resizing is more trivial, but isn't the interesting use case. Hence
    limit ring resizing in general to DEFER_TASKRUN only for now. This isn't
    a huge problem as CQ ring resizing is generally the most useful on
    networking type of workloads where it can be hard to size the ring
    appropriately upfront, and those should be using DEFER_TASKRUN for
    better performance.

    Fixes: 79cfe9e ("io_uring/register: add IORING_REGISTER_RESIZE_RINGS")
    Signed-off-by: Jens Axboe <[email protected]>

Signed-off-by: Ming Lei <[email protected]>

Author: Ming Lei

io_uring/register.c

@@ -414,6 +414,9 @@ static int io_register_resize_rings(struct io_ring_ctx *ctx, void __user *arg)
 	if (ctx->flags & IORING_SETUP_SINGLE_ISSUER &&
 	    current != ctx->submitter_task)
 		return -EEXIST;
+	/* limited to DEFER_TASKRUN for now */
+	if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
+		return -EINVAL;
 	if (copy_from_user(&p, arg, sizeof(p)))
 		return -EFAULT;
 	if (p.flags & ~RESIZE_FLAGS)