Re: [PATCH] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[Caleb Sander Mateos <csander@purestorage.com>]

On Fri, Oct 17, 2025 at 5:41 AM Alok Tiwari <alok.a.tiwari@oracle.com> wrote:
>
> The negation operator incorrectly places outside the unlikely() macro:
>
>     if (!unlikely(iwa))
>
> This caused the compiler hint to be applied to the constant result
> of the negation rather than the pointer check itself.

Not sure what you mean by "constant". But yes, applying !unlikely(iwa)
inverts the hint, saying iwa is unlikely to be non-NULL and therefore
the if branch is likely. It certainly seems more likely that the whole
if condition was meant to me marked unlikely.

Best,
Caleb

>
> Fix it by moving the negation inside unlikely(), matching the usual
> kernel pattern:
>
>     if (unlikely(!iwa))
>
> Fixes: 2b4fc4cd43f2 ("io_uring/waitid: setup async data in the prep handler")
> Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
> ---
>  io_uring/waitid.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/io_uring/waitid.c b/io_uring/waitid.c
> index f25110fb1b12..53532ae6256c 100644
> --- a/io_uring/waitid.c
> +++ b/io_uring/waitid.c
> @@ -250,7 +250,7 @@ int io_waitid_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>                 return -EINVAL;
>
>         iwa = io_uring_alloc_async_data(NULL, req);
> -       if (!unlikely(iwa))
> +       if (unlikely(!iwa))
>                 return -ENOMEM;
>         iwa->req = req;
>
> --
> 2.50.1
>
>