Re: [patch V4 10/12] futex: Convert to scoped user access

From: Thomas Gleixner <tglx@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
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	linux-fsdevel@vger.kernel.org
Subject: Re: [patch V4 10/12] futex: Convert to scoped user access
Date: Thu, 23 Oct 2025 20:44:13 +0200	[thread overview]
Message-ID: <873479xxtu.ffs@tglx> (raw)
In-Reply-To: <CAHk-=wgLAJuJ8SP8NiSGbXJQMdxiPkBN32EvAy9R8kCnva4dfg@mail.gmail.com>

On Wed, Oct 22 2025 at 05:16, Linus Torvalds wrote:
> On Wed, 22 Oct 2025 at 02:49, Thomas Gleixner <tglx@linutronix.de> wrote:
>>
>> From: Thomas Gleixner <tglx@linutronix.de>
>>
>> Replace the open coded implementation with the new get/put_user_scoped()
>> helpers.
>
> Well, "scoped" here makes no sense in the name, since it isn't scoped
> in any way, it just uses the scoped helpers.

I know. Did not come up with a sensible name so far.

> I also wonder if we should just get rid of the futex_get/put_value()
> macros entirely. I did those masked user access things them long ago
> because that code used "__get_user()" and "__put_user()", and I was
> removing those helpers and making it match the pattern elsewhere, but
> I do wonder if there is any advantage left to them all.
>
> On x86, just using "get_user()" and "put_user()" should work fine now.
> Yes, they check the address, but these days *those* helpers use that
> masked user address trick too, so there is no real cost to it.
>
> The only cost would be the out-of-line function call, I think. Maybe
> that is a sufficiently big cost here.

I'll have a look at the usage sites.

But as you said out-of-line function call it occured to me that these
helpers might be just named get/put_user_inline(). Hmm?

Thanks,

        tglx