From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1DFEC282E1 for ; Fri, 24 May 2019 11:18:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A0A821773 for ; Fri, 24 May 2019 11:18:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="dWcgLrZo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390876AbfEXLSk (ORCPT ); Fri, 24 May 2019 07:18:40 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:37842 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390759AbfEXLSk (ORCPT ); Fri, 24 May 2019 07:18:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=MwsXLs7WTZaHxJpnrqoGN4CLjyg7waRkeF8Z+h9pCfA=; b=dWcgLrZoVDg62DirK77o+eC7x wxkOHptuRv34IPZg2fqfuDEf6hyMn/LD2xO3ZHyILpKXC4tM1ngwnCthGFgR2rIjAWHT/GVmnF51O 1yda5LCb1txf0XlYovXt7RubaokJKOGKRXr5RJYNoU6VLvd89D8nCREMM4DgNYog35uIJ9vf3o3fh 7QE0auEW8jgKa/i90HKXp8nCDU7WZS/tRqSRwAikitk5LLL048PsizIudFbJSH22Gj9cnwNvaivMz tlaUJ6NGTbuwHEderejD+yg0bd41IniWaRXaxxYQ/2IPEiBCBLImAfvTpBuinnxJV/lOdKBvzVuWu tvdK2oLSg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hU8DB-0007nx-Ar; Fri, 24 May 2019 11:18:09 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A486A2029B0A3; Fri, 24 May 2019 13:18:07 +0200 (CEST) Date: Fri, 24 May 2019 13:18:07 +0200 From: Peter Zijlstra To: Mark Rutland Cc: Andrea Parri , linux-kernel@vger.kernel.org, will.deacon@arm.com, aou@eecs.berkeley.edu, arnd@arndb.de, bp@alien8.de, catalin.marinas@arm.com, davem@davemloft.net, fenghua.yu@intel.com, heiko.carstens@de.ibm.com, herbert@gondor.apana.org.au, ink@jurassic.park.msu.ru, jhogan@kernel.org, linux@armlinux.org.uk, mattst88@gmail.com, mingo@kernel.org, mpe@ellerman.id.au, palmer@sifive.com, paul.burton@mips.com, paulus@samba.org, ralf@linux-mips.org, rth@twiddle.net, stable@vger.kernel.org, tglx@linutronix.de, tony.luck@intel.com, vgupta@synopsys.com, gregkh@linuxfoundation.org, jhansen@vmware.com, vdasa@vmware.com, aditr@vmware.com, Steven Rostedt Subject: Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup Message-ID: <20190524111807.GS2650@hirez.programming.kicks-ass.net> References: <20190522132250.26499-1-mark.rutland@arm.com> <20190523083013.GA4616@andrea> <20190523101926.GA3370@lakrids.cambridge.arm.com> <20190524103731.GN2606@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190524103731.GN2606@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 24, 2019 at 12:37:31PM +0200, Peter Zijlstra wrote: > On Thu, May 23, 2019 at 11:19:26AM +0100, Mark Rutland wrote: > > > [mark@lakrids:~/src/linux]% git grep '\(return\|=\)\s\+atomic\(64\)\?_set' > > include/linux/vmw_vmci_defs.h: return atomic_set((atomic_t *)var, (u32)new_val); > > include/linux/vmw_vmci_defs.h: return atomic64_set(var, new_val); > > > > Oh boy, what a load of crap you just did find. > > How about something like the below? I've not read how that buffer is > used, but the below preserves all broken without using atomic*_t. Clarified by something along these lines? --- Documentation/atomic_t.txt | 3 +++ 1 file changed, 3 insertions(+) diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt index dca3fb0554db..125c95ddbbc0 100644 --- a/Documentation/atomic_t.txt +++ b/Documentation/atomic_t.txt @@ -83,6 +83,9 @@ The non-RMW ops are (typically) regular LOADs and STOREs and are canonically implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and smp_store_release() respectively. +Therefore, if you find yourself only using the Non-RMW operations of atomic_t, +you do not in fact need atomic_t at all and are doing it wrong. + The one detail to this is that atomic_set{}() should be observable to the RMW ops. That is: