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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 6BF9DC2BA83 for ; Thu, 13 Feb 2020 09:16:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3D36920848 for ; Thu, 13 Feb 2020 09:16:59 +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="ku/BpLGK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729808AbgBMJQ6 (ORCPT ); Thu, 13 Feb 2020 04:16:58 -0500 Received: from merlin.infradead.org ([205.233.59.134]:40866 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729531AbgBMJQ6 (ORCPT ); Thu, 13 Feb 2020 04:16:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=4vhmf3DfYgCxxMcfNakVANw6c8V541MWMOKqcLRnwZ4=; b=ku/BpLGKwsgfbGC6UpccsJkusm ohh433d8dfXGfwe16+tgYPg8Bfs61/UNrURkxYS7FjkBPNij3Wn3RTdmj4bIrXTWyuKkhUhS5of1Y e1nsY7NFhV4UFXAkDgWrZWsnNfgt+1QiOxVuS6aWjEljsaFE2XdaySBm/ErnGeOkQWXOUqCHB0DNr dSIj1/lXMIyyOOxfUS8NIbzdx4vNDe2tEBc+nJiV4Hd48pwGs2LEVEvU+sUxotJ7PiaAsU1bxw9kY TacLjLVvSIgJqcov7PVb66TaEHWfGB1x3byc4bDZRzZNcV3yLpeiVM/omvElhYtBhMaabCAdPeNFO VMcDT38g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j2AcA-0006XK-6X; Thu, 13 Feb 2020 09:16:54 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 278B930066E; Thu, 13 Feb 2020 10:15:02 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B2FCC2B2E4991; Thu, 13 Feb 2020 10:16:51 +0100 (CET) Date: Thu, 13 Feb 2020 10:16:51 +0100 From: Peter Zijlstra To: Michal Simek Cc: linux-kernel@vger.kernel.org, monstr@monstr.eu, git@xilinx.com, arnd@arndb.de, Stefan Asserhall load and store , Boqun Feng , Will Deacon , paulmck@kernel.org Subject: Re: [PATCH 7/7] microblaze: Do atomic operations by using exclusive ops Message-ID: <20200213091651.GA14946@hirez.programming.kicks-ass.net> References: <20200212155500.GB14973@hirez.programming.kicks-ass.net> <4b46b33e-14ad-7097-f0db-2915ac772f15@xilinx.com> <20200213085849.GL14897@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213085849.GL14897@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 Thu, Feb 13, 2020 at 09:58:49AM +0100, Peter Zijlstra wrote: > The thing is, your bog standard LL/SC _SHOULD_ fail the SC if someone > else does a regular store to the same variable. See the example in > Documentation/atomic_t.txt. > > That is, a competing SW/SWI should result in the interconnect responding > with something other than EXOKAY, the SWX should fail and MSR[C] <- 1. The thing is; we have code that relies on this behaviour. There are a few crusty SMP archs that sorta-kinda limp along (mostly by disabling some of the code and praying the rest doesn't trigger too often), but we really should not allow more broken SMP archs.