Message-ID: <f7d9194b-6681-48f0-b5e9-11f43d2849bd@collabora.com>
Date:   Mon, 6 Dec 2021 09:12:11 -0300
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Subject: Re: [PATCH] futex: Fix a faulty comment.
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To:     6812skiii@gmail.com
Cc:     peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de,
        dvhart@infradead.org, dave@stgolabs.net,
        linux-kernel@vger.kernel.org
References: <20211204181458.10076-1-6812skiii@gmail.com>
From:   =?UTF-8?Q?Andr=c3=a9_Almeida?= <andrealmeid@collabora.com>
In-Reply-To: <20211204181458.10076-1-6812skiii@gmail.com>
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Hi Jangwoong,

Thanks for your patch! However...

Às 15:14 de 04/12/21, 6812skiii@gmail.com escreveu:
> From: Jangwoong Kim <6812skiii@gmail.com>
> 
> We return 1, not the index of futex woken up.
> 
> Signed-off-by: Jangwoong Kim <6812skiii@gmail.com>
> ---
>  kernel/futex/waitwake.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
> index 4ce0923f1ce3..d148e5d4956b 100644
> --- a/kernel/futex/waitwake.c
> +++ b/kernel/futex/waitwake.c
> @@ -455,8 +455,8 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
>  
>  		/*
>  		 * Even if something went wrong, if we find out that a futex
> -		 * was woken, we don't return error and return this index to
> -		 * userspace
> +		 * was woken, we don't return error and make userspace aware
> +		 * of this by returning 1.

We return to userspace the value at *woken, so your fix is wrong. Have a
look at futex_wait_multiple():

		ret = futex_wait_multiple_setup(vs, count, &hint);
		if (ret) {
			if (ret > 0) {
				/* A futex was woken during setup */
				ret = hint;
			}
			return ret;
		}

When we return 1 at futex_wait_multiple_setup(), we end up returning the
hint/woken value to userspace.

Let me know if you have questions.

	André