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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 0D0E5C433E2 for ; Tue, 15 Sep 2020 22:32:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C83CD20809 for ; Tue, 15 Sep 2020 22:32:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600209145; bh=OqNo4S1pwXf0y+OZFi5cbHnZ01UaP3lAlNY279lhRwE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=rn/zna1vcyi1H3XDt9aPmMnlepZ0xvBcydROlOCxNH8uFm34JDqZhmB7YP/R/EO3w e0e2jd6D6Nx0TvJA++UnpLIXoiHI5tor5N6sdVbG+XfvXLu2PNJRhyvOdKuno002xH Fd7ysuXV8PYlgZ9KwqQ94w6s1XzvejM8ZUAT5psE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727649AbgIOWbx (ORCPT ); Tue, 15 Sep 2020 18:31:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:59530 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727503AbgIOQRT (ORCPT ); Tue, 15 Sep 2020 12:17:19 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D468E21D24; Tue, 15 Sep 2020 16:11:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600186288; bh=OqNo4S1pwXf0y+OZFi5cbHnZ01UaP3lAlNY279lhRwE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1SbAjFtsROiRCnu7dWyqN1sIRZoFtHLH0MUJUYOlqDz9sybYMVk7vMa97tuhN/eXb 2X+dts4/sCSWx68z5lSHzmqQDfHvyzZxYUgNpCa4RxG/Ut4m70Zks3irGDXZRCVYTp oAQBm5qwIMsvFOtlPHV50y+STKCjMdNmVH4jbBoc= Date: Tue, 15 Sep 2020 17:11:23 +0100 From: Will Deacon To: peterz@infradead.org Cc: Oleg Nesterov , Hou Tao , Ingo Molnar , Dennis Zhou , Tejun Heo , Christoph Lameter , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jan Kara Subject: Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count Message-ID: <20200915161123.GC26745@willie-the-truck> References: <20200915140750.137881-1-houtao1@huawei.com> <20200915150610.GC2674@hirez.programming.kicks-ass.net> <20200915153113.GA6881@redhat.com> <20200915155150.GD2674@hirez.programming.kicks-ass.net> <20200915160344.GH35926@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200915160344.GH35926@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 Tue, Sep 15, 2020 at 06:03:44PM +0200, peterz@infradead.org wrote: > On Tue, Sep 15, 2020 at 05:51:50PM +0200, peterz@infradead.org wrote: > > > Anyway, I'll rewrite the Changelog and stuff it in locking/urgent. > > How's this? > > --- > Subject: locking/percpu-rwsem: Use this_cpu_{inc,dec}() for read_count > From: Hou Tao > Date: Tue, 15 Sep 2020 22:07:50 +0800 > > From: Hou Tao > > The __this_cpu*() accessors are (in general) IRQ-unsafe which, given > that percpu-rwsem is a blocking primitive, should be just fine. > > However, file_end_write() is used from IRQ context and will cause > load-store issues. ... on architectures where the per-cpu accessors are not atomic. > > Fixing it by using the IRQ-safe this_cpu_*() for operations on Fixing => Fix ? > read_count. This will generate more expensive code on a number of > platforms, which might cause a performance regression for some of the > other percpu-rwsem users. > > If any such is reported, we can consider alternative solutions. > > Fixes: 70fe2f48152e ("aio: fix freeze protection of aio writes") > Signed-off-by: Hou Tao > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lkml.kernel.org/r/20200915140750.137881-1-houtao1@huawei.com > --- > include/linux/percpu-rwsem.h | 8 ++++---- > kernel/locking/percpu-rwsem.c | 4 ++-- > 2 files changed, 6 insertions(+), 6 deletions(-) For the patch: Acked-by: Will Deacon Will