From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1F24E192580 for ; Mon, 28 Oct 2024 10:46:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730112408; cv=none; b=qMKG3PlZ7yybK0V224HOLjGmTmCWUUJN2IWFttO7622u/0spiXiC20Fg7a1WNEsdVFisuCZSgaVZIE2lZYYmTljJb4gZ7kEiVSTsp6iXdm+Y/XH0+EfIuhaMVHnfKsSC3Qe6auFJou9aaULKqwS7gx9SRL7eaNyf8jzykzdRPNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730112408; c=relaxed/simple; bh=uqGd+5K0IS/guLWphRp8p0UNHM8STaKdQNsrlDdqgzA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qSO9X9jKIAy0bhfIOugyEQUmFuyK3guqDAXXg6OboEW+FDkieT48sAvJMDFsHq9H95OwnPXxx1dSUcFm4Xutq6dNK2r+9XG2fK72XhtxzRBqm/0SaZFzs0K6y1KNj5LnCK7gdxgFMjAyQDmuVcFfOK4a8KEUwElzKmz2/cNVa+I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=tEaP/Jro; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="tEaP/Jro" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=aNBVnpnxclIi2HMW+gqI4liCLPIUUouhrXh4IESKQEk=; b=tEaP/JrogOSGYT/n7wYKCBaFJW MK3RHTold6i6rBJV+/CfwbThE8T3PYHbL+UKWyHYRMmkotZTmv6ge+CURmjJeiyBbHc6rUW9MNeFh ZnN2I5wsZRsgkm5P9N2UzkGC86uyUclz4E7PmeVg4Bp+Ub3Uds1fwAONyrTQ/KCCh3gROLhD7FFRW 8zOWY6uNsxZWVrOPQoD8/qMr48NKvQqOemGgLE4jwH0EjkDMK8rcnZsb8MfnD03lZNe+94fpisg8d b8dVvUL336ZGrrv/kRf5zwsFESAMj/RsdwRnH7GXscBPO3VIuzJRoXirV9dRC/CNS1i9fzOU6hLJR CFxGE4lg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1t5NGh-00000008IHC-2H5A; Mon, 28 Oct 2024 10:46:40 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 7155030083E; Mon, 28 Oct 2024 11:46:39 +0100 (CET) Date: Mon, 28 Oct 2024 11:46:39 +0100 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, =?iso-8859-1?Q?Andr=E9?= Almeida , Darren Hart , Davidlohr Bueso , Ingo Molnar , Juri Lelli , Valentin Schneider , Waiman Long Subject: Re: [RFC PATCH 2/3] futex: Add basic infrastructure for local task local hash. Message-ID: <20241028104639.GO9767@noisy.programming.kicks-ass.net> References: <20241026224306.982896-1-bigeasy@linutronix.de> <20241026224306.982896-3-bigeasy@linutronix.de> <20241028101633.GM9767@noisy.programming.kicks-ass.net> <20241028102408.GbFgnLMF@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241028102408.GbFgnLMF@linutronix.de> On Mon, Oct 28, 2024 at 11:24:08AM +0100, Sebastian Andrzej Siewior wrote: > On 2024-10-28 11:16:33 [+0100], Peter Zijlstra wrote: > > On Sun, Oct 27, 2024 at 12:34:51AM +0200, Sebastian Andrzej Siewior wrote: > > > > > Introduce a task local hash map. The hashmap can be allocated via > > > prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_ALLOCATE, 0) > > > > Per process, per task is useless and will make things malfunction. > > > > Things missing in this patch are CLONE_THREAD / CLONE_VM, and create > > must be absolutely forbidden once mm_users != 1. > > I moved this to struct signal_struct and limited it for now to the > group leader. That works I suppose. 'process' is a really dodgy thing in Linux anyway :/ So CLONE_THREAD implies CLONE_SIGHAND, and CLONE_SIGHAND in turn implies CLONE_VM -- however, you can do CLONE_VM without either SIGHAND or THREAD, (or SIGHAND|VM without THREAD). And it all quickly becomes a real mess. 'Sane' userspace doesn't play such games, and insane userspace gets to keep the pieces I suppose.