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

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Message-ID: <873479xxtu.ffs@tglx>
Date: Thu, 23 Oct 2025 20:44:13 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra
 <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>, Davidlohr
 Bueso <dave@...olabs.net>, André Almeida
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 <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, Nicholas
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 <christophe.leroy@...roup.eu>, linuxppc-dev@...ts.ozlabs.org, Paul
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 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 linux-fsdevel@...r.kernel.org
Subject: Re: [patch V4 10/12] futex: Convert to scoped user access

On Wed, Oct 22 2025 at 05:16, Linus Torvalds wrote:
> On Wed, 22 Oct 2025 at 02:49, Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> From: Thomas Gleixner <tglx@...utronix.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