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bh=zmlfoRcUVyyK6VDWwuqIXZu4oD0M/UoDbT+qIU6ZUP8=; b=GNkr4yO9Wh8utq3Zt2tM8NULxbMTdkTTfxsbR2e7JLp8ip1wDgEg99qZ6Q+4xpHY5ny9Ma s6aSDxn89YCUHl3ChYtUZuJfgtQMf5XsnydZ9VxOJqmZubHu9Ftk/t5q/b0BsYeL3/J708 v6DWbT7qwiaEeswVAw3hUjuG8Nu2wZOZHkEeZcfxAV9RZsGivU+YfOCzlFE10X+O1hmwPd /2q8QWfz6eFy5qdiTk+OadjzLVW/reZOUBq/disMAW4+Tu642/kOahCDrGkJDO06vVihL3 OA3hjqU3HUz81tK2ZWcLLCckYPC2oMlZoH80PE+8u8hc4Ny8HwjDw6XZd5NWqQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1690838051; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zmlfoRcUVyyK6VDWwuqIXZu4oD0M/UoDbT+qIU6ZUP8=; b=wB5Xf+Iq3rcAu4YpX7kKXKT+wmsUYdpedrVysKtZQz/odp4Xuif6wYETOyAZgFE/eynJ7H qIMRzrxdAOliZkCw== To: Peter Zijlstra Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, mingo@redhat.com, dvhart@infradead.org, dave@stgolabs.net, andrealmeid@igalia.com, Andrew Morton , urezki@gmail.com, hch@infradead.org, lstoakes@gmail.com, Arnd Bergmann , linux-api@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, malteskarupke@web.de Subject: Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags In-Reply-To: <20230731192012.GA11704@hirez.programming.kicks-ass.net> References: <20230721102237.268073801@infradead.org> <20230721105743.819362688@infradead.org> <87edkonjrk.ffs@tglx> <87mszcm0zw.ffs@tglx> <20230731192012.GA11704@hirez.programming.kicks-ass.net> Date: Mon, 31 Jul 2023 23:14:11 +0200 Message-ID: <87a5vbn5r0.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 04B9FC0014 X-Stat-Signature: ucprdhrwh1g9h7jtwerd83i43kacpkir X-HE-Tag: 1690838053-158679 X-HE-Meta: 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 ZlP3Qmjm +YaXGvDMUCEq/07+7V+5Ui8J6Q1S8Xbw4ZJcNtYFfTtentFI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 31 2023 at 21:20, Peter Zijlstra wrote: > -#define FUTEX2_MASK (FUTEX2_64 | FUTEX2_PRIVATE) > +#define FUTEX2_MASK (FUTEX2_SIZE_MASK | FUTEX2_PRIVATE) Along with some comment which documents that the size "flags" constitute a number field and not flags in the sense of binary flags. And please name these size constants so it really becomes obvious: #define FUTEX2_SIZE_U32 2 > /** > * futex_parse_waitv - Parse a waitv array from userspace > @@ -208,11 +208,11 @@ static int futex_parse_waitv(struct fute > return -EINVAL; > > if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) { > - if ((aux.flags & FUTEX2_64) == FUTEX2_64) > + if ((aux.flags & FUTEX2_SIZE_MASK) == FUTEX2_64) > return -EINVAL; > } That should be part of the actual 64bit futex enablement, no? > - if ((aux.flags & FUTEX2_64) != FUTEX2_32) > + if ((aux.flags & FUTEX2_SIZE_MASK) != FUTEX2_32) > return -EINVAL; In hindsight I think it was as mistake just to have this __u32 flags field in the new interface. Soemthing like the incomplete below might be retrofittable, no? --- a/include/uapi/linux/futex.h +++ b/include/uapi/linux/futex.h @@ -74,7 +74,12 @@ struct futex_waitv { __u64 val; __u64 uaddr; - __u32 flags; + union { + __u32 flags; + __u32 size : 2, + : 5, + private : 1; + }; __u32 __reserved; }; --- a/kernel/futex/syscalls.c +++ b/kernel/futex/syscalls.c @@ -204,10 +204,10 @@ static int futex_parse_waitv(struct fute if (copy_from_user(&aux, &uwaitv[i], sizeof(aux))) return -EFAULT; - if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved) + if ((aux.flags & ~FUTEX2_VALID_FLAGBITS) || aux.__reserved) return -EINVAL; - if (!(aux.flags & FUTEX2_32)) + if (aux.size != FUTEX2_SIZE_U32) return -EINVAL; futexv[i].w.flags = aux.flags; If this muck already confused me right now, then I don't want to experience the confusion factor 6 month down the road :) Thanks, tglx