linux-kernel - Re: [RFC PATCH 01/13] futex2: Implement wait and wake functions

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Date:   Thu, 18 Feb 2021 10:48:50 -0500
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     André Almeida <andrealmeid@...labora.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        kernel@...labora.com, pgriffais@...vesoftware.com,
        z.figura12@...il.com, joel@...lfernandes.org,
        malteskarupke@...tmail.fm, linux-api@...r.kernel.org,
        fweimer@...hat.com, libc-alpha@...rceware.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org, acme@...nel.org,
        corbet@....net
Subject: Re: [RFC PATCH 01/13] futex2: Implement wait and wake functions

André Almeida <andrealmeid@...labora.com> writes:

>>> +		if (unlikely(ret)) {
>>> +			spin_unlock(&bucket->lock);
>>> +
>>> +			bucket_dec_waiters(bucket);
>>> +			__set_current_state(TASK_RUNNING);
>>> +			*awakened = futex_dequeue_multiple(futexv, i);
>>> +
>>> +			if (__get_user(uval, uaddr))
>>> +				return -EFAULT;
>>> +
>>> +			if (*awakened >= 0)
>>> +				return 1;
>> If you are awakened, you don't need to waste time with trying to get
>> the
>> next key.
>> 
>
> Yes, and this is what this return is supposed to do. What I'm missing?

you don't need to do that __get_user if some other key was already awoke.

[...]
if (*awakened >= 0)
	return 1;

if (__get_user(uval, uaddr))
	return -EFAULT;
[...]

-- 
Gabriel Krisman Bertazi