Re: [PATCH 06/10] io_uring: add support for futex wake and wait

[Peter Zijlstra]

On Fri, Jul 21, 2023 at 09:29:14AM -0600, Jens Axboe wrote:

> FWIW, here's the io_uring incremental after that rebase. Update the
> liburing futex branch as well, updating the prep helpers to take 64 bit
> values for mask/val and also add the flags argument that was missing as
> well. Only other addition was adding those 4 new patches instead of the
> old 3 ones, and adding single patch that just moves FUTEX2_MASK to
> futex.h.
> 
> All checks out fine, tests pass and it works.
> 
> 
> diff --git a/io_uring/futex.c b/io_uring/futex.c
> index 93df54dffaa0..4c9f2c841b98 100644
> --- a/io_uring/futex.c
> +++ b/io_uring/futex.c
> @@ -18,11 +18,11 @@ struct io_futex {
>  		u32 __user			*uaddr;
>  		struct futex_waitv __user	*uwaitv;
>  	};
> +	unsigned long	futex_val;
> +	unsigned long	futex_mask;
>  	unsigned long	futexv_owned;
> +	u32		futex_flags;
> +	unsigned int	futex_nr;
>  };
>  
>  struct io_futex_data {
> @@ -171,15 +171,28 @@ bool io_futex_remove_all(struct io_ring_ctx *ctx, struct task_struct *task,
>  int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  {
>  	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
> +	u32 flags;
>  
> +	if (unlikely(sqe->fd || sqe->buf_index || sqe->file_index))
>  		return -EINVAL;
>  
>  	iof->uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
> +	iof->futex_val = READ_ONCE(sqe->addr2);
> +	iof->futex_mask = READ_ONCE(sqe->addr3);
> +	iof->futex_nr = READ_ONCE(sqe->len);
> +	if (iof->futex_nr && req->opcode != IORING_OP_FUTEX_WAITV)
> +		return -EINVAL;
> +

Hmm, would something like:

	if (req->opcode == IORING_OP_FUTEX_WAITV) {
		if (iof->futex_val && iof->futex_mask)
			return -EINVAL;

		/* sys_futex_waitv() doesn't take @flags as of yet */
		if (iof->futex_flags)
			return -EINVAL;

		if (!iof->futex_nr)
			return -EINVAL;

	} else {
		/* sys_futex_{wake,wait}() don't take @nr */
		if (iof->futex_nr)
			return -EINVAL;

		/* both take @flags and @mask */
		flags = READ_ONCE(sqe->futex_flags);
		if (flags & ~FUTEX2_MASK)
			return -EINVAL;

		iof->futex_flags = futex2_to_flags(flags);
		if (!futex_flags_valid(iof->futex_flags))
			return -EINVAL;

		if (!futex_validate_input(iof->futex_flags, iof->futex_mask))
			return -EINVAL;

		/* sys_futex_wait() takes @val */
		if (req->iocode == IORING_OP_FUTEX_WAIT) {
			if (!futex_validate_input(iof->futex_flags, iof->futex_val))
				return -EINVAL;
		} else {
			if (iof->futex_val)
				return -EINVAL;
		}
	}

work? The waitv thing is significantly different from the other two.