From: "André Almeida" <andrealmeid@collabora.com>
To: Jangwoong Kim <6812skiii@gmail.com>
Cc: peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de,
dvhart@infradead.org, dave@stgolabs.net,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] futex: Fix a faulty comment.
Date: Mon, 6 Dec 2021 17:34:56 -0300 [thread overview]
Message-ID: <8a7cc760-b1e2-0da6-f3cc-4e7baa3d956c@collabora.com> (raw)
In-Reply-To: <CAF=mnpi65WtnK_mF1f8GfMEczS1ruj8q4YbA18R5KvWcpkxLxw@mail.gmail.com>
Hi Jangwoong,
Please don't top post when replying to emails in this list (read more
here: https://www.mediawiki.org/wiki/Mailing_list_etiquette)
Às 14:44 de 06/12/21, Jangwoong Kim escreveu:
> Hi André.
>
> That patch was definitely wrong, I apologize.
>
> However, since futex_wait_multiple_setup() sets the last index of
> futex that was woken up,
> shouldn't the comment be modified as below?
>
> If so, I will resend a patch.
>
> /*
> - * 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
> + * Even if something went wrong, if we find out that any futex
> + * was woken, we don't return error and return the last index
> + * awoken to userspace
Indeed, this is more correct. You can send a patch to clarify this comment.
> */
> *woken = unqueue_multiple(vs, i);
> if (*woken >= 0)
>
> I sent the patch because I thought this was important enough to be corrected.
>
> Let me know If this is not crucial enough to be patched, so I won't
> keep sending comment-fixing patches.
>
> Thank you.
> Jangwoong Kim.
>
> 2021년 12월 6일 (월) 오후 9:12, André Almeida <andrealmeid@collabora.com>님이 작성:
>>
>> 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
prev parent reply other threads:[~2021-12-06 20:35 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-04 18:14 [PATCH] futex: Fix a faulty comment 6812skiii
2021-12-06 12:12 ` André Almeida
2021-12-06 17:44 ` Jangwoong Kim
2021-12-06 20:34 ` André Almeida [this message]
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