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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 BDE26C10F14 for ; Tue, 23 Apr 2019 13:40:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C659214AE for ; Tue, 23 Apr 2019 13:40:14 +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="AR67rJjv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727799AbfDWNkN (ORCPT ); Tue, 23 Apr 2019 09:40:13 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49504 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726801AbfDWNkN (ORCPT ); Tue, 23 Apr 2019 09:40:13 -0400 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: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=y5x4SrRuOG6KqEv5SjoNKrRwTXVCdGEbhb9XQVsw16c=; b=AR67rJjv+UP1eHVJ2VGR1yZ1v TatE9hy4a62FXAqrTQjkOZ19cdYnX+aNt29yIWRQ9LmlV+1YnFkji6rG2QQs4yNhcUij7gdW10W0u fwodHhgs7DO628bPda+qCDSgB9y9bTv5mSM6KpXM5egVrlL3o8osyZ3fK/oxTD99EVlt7idE32obZ d/X7UFwLcQdAYpOPWZBHWoIweAj7Ly6piCBiB2K6RhfTwLjvruInpjd/aWu+IFkO05Op2cl6ZDzZ9 6QQ0yDJ30d0zpkhcwCks/uMgWCJfQxULQkZngC6eozsUQOehT95VwHMf7qxLCZNTLnmOApCR6h0RI WbHURFUcQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hIveW-0004xz-EL; Tue, 23 Apr 2019 13:40:04 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 35D6529C2338C; Tue, 23 Apr 2019 15:40:03 +0200 (CEST) Date: Tue, 23 Apr 2019 15:40:03 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Nicholas Piggin , LKMM Maintainers -- Akira Yokosawa , Andrea Parri , Boqun Feng , David Howells , Daniel Lustig , Jade Alglave , Kernel development list , Luc Maranget , Alan Stern , Will Deacon Subject: Re: [PATCH] Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}_atomic() Message-ID: <20190423134003.GV4038@hirez.programming.kicks-ass.net> References: <20190419180017.GP4038@hirez.programming.kicks-ass.net> <20190419182620.GF14111@linux.ibm.com> <1555719429.t9n8gkf70y.astroid@bobo.none> <20190420085440.GK14111@linux.ibm.com> <20190423123209.GR4038@hirez.programming.kicks-ass.net> <20190423133010.GK3923@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190423133010.GK3923@linux.ibm.com> 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 Tue, Apr 23, 2019 at 06:30:10AM -0700, Paul E. McKenney wrote: > There are a great many that look like this: > > smp_mb__before_atomic(); > clear_bit(NFSD4_CLIENT_UPCALL_LOCK, &clp->cl_flags); > smp_mb__after_atomic(); Ooh, marvel at the comment describing the ordering there. Oh wait :-( So much for checkpatch.pl I suppose. I think the first is a release order for the 'LOCK' bit and the second is because of wake_up_bit() being a shitty interface. So maybe that should've been: clear_bit_unlock(NFSD4_CLIENT_UPCALL_LOCK, &clp->cl_flags); smp_mb__after_atomic(); wake_up_bit(&clp->cl_flags, NFSD4_CLIENT_UPCALL_LOCK); instead?