[PATCH v2] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[PATCH v2] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[Alok Tiwari]

The negation operator incorrectly places outside the unlikely() macro:

    if (!unlikely(iwa))

This inverted the compiler branch prediction hint, marking the NULL
case as likely instead of unlikely. The intent is to indicate that
allocation failures are rare, consistent with common kernel patterns.

 Moving the negation inside unlikely():

    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>
---
v1 -> v2
Remove misleading "constant result" wording and
rephrase commit message
--
 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

Re: [PATCH v2] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[Caleb Sander Mateos]

On Sat, Oct 18, 2025 at 12:33 PM Alok Tiwari <alok.a.tiwari@oracle.com> wrote:
>
> The negation operator incorrectly places outside the unlikely() macro:

"incorrectly places" -> "is incorrectly placed"?

>
>     if (!unlikely(iwa))
>
> This inverted the compiler branch prediction hint, marking the NULL
> case as likely instead of unlikely. The intent is to indicate that
> allocation failures are rare, consistent with common kernel patterns.
>
>  Moving the negation inside unlikely():
>
>     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>

Other than that,
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>

> ---
> v1 -> v2
> Remove misleading "constant result" wording and
> rephrase commit message
> --
>  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
>

Re: [PATCH v2] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[Jens Axboe]

On 10/19/25 10:27 AM, Caleb Sander Mateos wrote:
> On Sat, Oct 18, 2025 at 12:33 PM Alok Tiwari <alok.a.tiwari@oracle.com> wrote:
>>
>> The negation operator incorrectly places outside the unlikely() macro:
> 
> "incorrectly places" -> "is incorrectly placed"?

Indeed, I did some slight commit message massaging while applying.

-- 
Jens Axboe

Re: [PATCH v2] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[Gabriel Krisman Bertazi]

Alok Tiwari <alok.a.tiwari@oracle.com> writes:

> The negation operator incorrectly places outside the unlikely() macro:
>
>     if (!unlikely(iwa))
>
> This inverted the compiler branch prediction hint, marking the NULL
> case as likely instead of unlikely. The intent is to indicate that
> allocation failures are rare, consistent with common kernel patterns.
>
>  Moving the negation inside unlikely():
>
>     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>

Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>


-- 
Gabriel Krisman Bertazi

Re: [PATCH v2] io_uring: fix incorrect unlikely() usage in io_waitid_prep()

[Jens Axboe]

On Sat, 18 Oct 2025 12:32:54 -0700, Alok Tiwari wrote:
> The negation operator incorrectly places outside the unlikely() macro:
> 
>     if (!unlikely(iwa))
> 
> This inverted the compiler branch prediction hint, marking the NULL
> case as likely instead of unlikely. The intent is to indicate that
> allocation failures are rare, consistent with common kernel patterns.
> 
> [...]

Applied, thanks!

[1/1] io_uring: fix incorrect unlikely() usage in io_waitid_prep()
      commit: 4ec703ec0c384a2199808c4eb2e9037236285a8d

Best regards,
-- 
Jens Axboe