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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 0F253C0018C for ; Mon, 7 Dec 2020 12:57:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C535723426 for ; Mon, 7 Dec 2020 12:57:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726174AbgLGM4x (ORCPT ); Mon, 7 Dec 2020 07:56:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725802AbgLGM4w (ORCPT ); Mon, 7 Dec 2020 07:56:52 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14A82C0613D1 for ; Mon, 7 Dec 2020 04:56:12 -0800 (PST) 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=YSUGplj7HrXl3d4m+FRlG+q1bwrz6RtuXMVuVA83zX0=; b=sJTwpfjFu/XeZCXuuKMRvg6WKa vOZcrdYm/QO59AkATkF12knuCPWcpX8e0NVmO7wvofmFywTSEyfDfp/BR9CtveMEAseHAegvQeOuk Zm2D72ng64AhHfdj2YYLrKAll5yfby/1sNbblgKQMsBh/HKGAxQkvBiDroVd5HRAqCo4QCpNdtZCo GJud4mNNOyHvOt0PUaBv6VSY8OnonwjsBj+VzQGAHxOYVzuWwu2xshFh4UY+kKjCBfC7e0O2Rmxb/ p0Ewfvb1rgFPSngfA+KtQFDDO/twB88H7KTvawenP6m2nPwGe1iyGzA0AAUO6WIgPAWrHgQIDKVtJ C3WZbZtA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmG3i-0004pU-Gv; Mon, 07 Dec 2020 12:56:06 +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 D852D301478; Mon, 7 Dec 2020 13:56:05 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id C2ED7200AAFCA; Mon, 7 Dec 2020 13:56:05 +0100 (CET) Date: Mon, 7 Dec 2020 13:56:05 +0100 From: Peter Zijlstra To: John Ogness Cc: Petr Mladek , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t Message-ID: <20201207125605.GN3040@hirez.programming.kicks-ass.net> References: <20201201205341.3871-1-john.ogness@linutronix.de> <20201201205341.3871-3-john.ogness@linutronix.de> <875z5eof8g.fsf@jogness.linutronix.de> <20201207093419.GH3040@hirez.programming.kicks-ass.net> <87mtyq9blw.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87mtyq9blw.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 07, 2020 at 11:09:39AM +0106, John Ogness wrote: > That will not work. We are talking about a situation where the writer is > preempted. So seq will never equal seq_copy in that situation. I expect > that the seqcount_latch is necessary. Interrupted rather, I would think, specifically NMIs? Then yes, latch should work. Gets you either the old or new, but never something in between.