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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A54BEB64D9 for ; Wed, 14 Jun 2023 11:28:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235934AbjFNL2q (ORCPT ); Wed, 14 Jun 2023 07:28:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243985AbjFNL2h (ORCPT ); Wed, 14 Jun 2023 07:28:37 -0400 Received: from out-53.mta0.migadu.com (out-53.mta0.migadu.com [91.218.175.53]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6CFF71BF9 for ; Wed, 14 Jun 2023 04:28:35 -0700 (PDT) MIME-Version: 1.0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1686742113; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cTaa5bkAAsCLeUbvEbbT4RXCgahfVxUJZ2KAppeaueI=; b=EjE6/y/cxxH5htYlmhMO86yXvD02DrutaaufHKu8Kjw8DC+9PZQvgzrHvEJo3ybV+HnnjJ 1tIEKaIPB0iBFLcX0p+yTkwNd2dfF//G5rTHgov8fNIlYlBcjH5BGtrwXuUNNKmaY5YFBh 8HvEwTlZJ6AkYhRWpDPkW+29HxNlcFA= Date: Wed, 14 Jun 2023 11:28:32 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: "Yajun Deng" Message-ID: Subject: Re: [PATCH] mm/mm_init.c: remove spinlock in early_pfn_to_nid() To: "Greg KH" Cc: rafael@kernel.org, rppt@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org In-Reply-To: <2023061431-litigate-upchuck-7ed1@gregkh> References: <2023061431-litigate-upchuck-7ed1@gregkh> <20230614110324.3839354-1-yajun.deng@linux.dev> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org June 14, 2023 7:09 PM, "Greg KH" wrote:=0A= =0A> On Wed, Jun 14, 2023 at 07:03:24PM +0800, Yajun Deng wrote:=0A> =0A>= > When the system boots, only one cpu is enabled before smp_init().=0A>> = So the spinlock is not needed in most cases, remove it.=0A>> =0A>> Add sp= inlock in get_nid_for_pfn() because it is after smp_init().=0A> =0A> So t= his is two different things at once in the same patch?=0A> =0A> Or are th= ey the same problem and both need to go in to solve it?=0A> =0A> And if a= spinlock is not needed at early boot, is it really causing any=0A> probl= ems?=0A> =0A=0AThey are the same problem.=0AI added pr_info in early_pfn_= to_nid(), found get_nid_for_pfn() is the only=0Acase need to add spinlock= .=0AThis patch tested on my x86 system.=0A=0A=0A>> Signed-off-by: Yajun D= eng =0A>> ---=0A>> drivers/base/node.c | 11 +++++++= ++--=0A>> mm/mm_init.c | 18 +++---------------=0A>> 2 files changed, 12 i= nsertions(+), 17 deletions(-)=0A>> =0A>> diff --git a/drivers/base/node.c= b/drivers/base/node.c=0A>> index 9de524e56307..844102570ff2 100644=0A>> = --- a/drivers/base/node.c=0A>> +++ b/drivers/base/node.c=0A>> @@ -748,8 += 748,15 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int ni= d)=0A>> static int __ref get_nid_for_pfn(unsigned long pfn)=0A>> {=0A>> #= ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT=0A>> - if (system_state < SYSTEM_R= UNNING)=0A>> - return early_pfn_to_nid(pfn);=0A>> + static DEFINE_SPINLOC= K(early_pfn_lock);=0A>> + int nid;=0A>> +=0A>> + if (system_state < SYSTE= M_RUNNING) {=0A>> + spin_lock(&early_pfn_lock);=0A>> + nid =3D early_pfn_= to_nid(pfn);=0A>> + spin_unlock(&early_pfn_lock);=0A> =0A> Adding an exte= rnal lock for when you call a function is VERY dangerous=0A> as you did n= ot document this anywhere, and there's no way to enforce it=0A> properly = at all.=0A> =0A=0AI should add a comment before early_pfn_to_nid().=0A=0A= > Does your change actually result in any boot time changes? How was this= =0A> tested?=0A> =0A=0AJust a bit.=0A=0A> thanks,=0A> =0A> greg k-h