linux-kernel - Re: [RFC][PATCH 04/10] futex: Add sys_futex

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Message-Id: <c5a09710-a7a1-43df-ac25-42e8f3983f9c@app.fastmail.com>
Date:   Fri, 14 Jul 2023 16:26:45 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Peter Zijlstra" <peterz@...radead.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Jens Axboe" <axboe@...nel.dk>
Cc:     linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...hat.com>,
        "Darren Hart" <dvhart@...radead.org>, dave@...olabs.net,
        andrealmeid@...lia.com,
        "Andrew Morton" <akpm@...ux-foundation.org>, urezki@...il.com,
        "Christoph Hellwig" <hch@...radead.org>,
        "Lorenzo Stoakes" <lstoakes@...il.com>, linux-api@...r.kernel.org,
        linux-mm@...ck.org, Linux-Arch <linux-arch@...r.kernel.org>,
        malteskarupke@....de
Subject: Re: [RFC][PATCH 04/10] futex: Add sys_futex_wake()

On Fri, Jul 14, 2023, at 15:39, Peter Zijlstra wrote:
>
> +++ b/include/linux/syscalls.h
> @@ -563,6 +563,9 @@ asmlinkage long sys_set_robust_list(stru
>  asmlinkage long sys_futex_waitv(struct futex_waitv *waiters,
>  				unsigned int nr_futexes, unsigned int flags,
>  				struct __kernel_timespec __user *timeout, clockid_t clockid);
> +
> +asmlinkage long sys_futex_wake(void __user *uaddr, int nr, unsigned 
> int flags, u64 mask);
> +

You can't really use 'u64' arguments in portable syscalls, it causes
a couple of problems, both with defining the user space wrappers,
and with compat mode.

Variants that would work include:

- using 'unsigned long' instead of 'u64'
- passing 'mask' by reference, as in splice()
- passing the mask in two u32-bit arguments like in llseek()

Not sure if any of the above work for you.

       Arnd