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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 DA070ECDFB4 for ; Wed, 18 Jul 2018 02:35:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E9AF20693 for ; Wed, 18 Jul 2018 02:35:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E9AF20693 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731698AbeGRDKj (ORCPT ); Tue, 17 Jul 2018 23:10:39 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:43962 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730614AbeGRDKj (ORCPT ); Tue, 17 Jul 2018 23:10:39 -0400 Received: from localhost.localdomain (c-24-4-125-7.hsd1.ca.comcast.net [24.4.125.7]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id E6F08BDB; Wed, 18 Jul 2018 02:35:05 +0000 (UTC) Date: Tue, 17 Jul 2018 19:35:04 -0700 From: Andrew Morton To: Omar Sandoval Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alexey Dobriyan , Eric Biederman , James Morse , Bhupesh Sharma , kernel-team@fb.com Subject: Re: [PATCH v2 1/7] proc/kcore: don't grab lock for kclist_add() Message-Id: <20180717193504.1d76fb1a43d0c8687d969143@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 12 Jul 2018 17:09:33 -0700 Omar Sandoval wrote: > From: Omar Sandoval > > kclist_add() is only called at init time, so there's no point in > grabbing any locks. We're also going to replace the rwlock with a rwsem, > which we don't want to try grabbing during early boot. > > ... > > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -62,6 +62,7 @@ static LIST_HEAD(kclist_head); > static DEFINE_RWLOCK(kclist_lock); > static int kcore_need_update = 1; > > +/* This doesn't grab kclist_lock, so it should only be used at init time. */ > void > kclist_add(struct kcore_list *new, void *addr, size_t size, int type) > { > @@ -69,9 +70,7 @@ kclist_add(struct kcore_list *new, void *addr, size_t size, int type) > new->size = size; > new->type = type; > > - write_lock(&kclist_lock); > list_add_tail(&new->list, &kclist_head); > - write_unlock(&kclist_lock); > } So we can mark kclist_add() as __init, yes? That way we save a scrap of ram and if someone starts calling kclist_add() from non-__init code we get a build-time warning. --- a/fs/proc/kcore.c~proc-kcore-dont-grab-lock-for-kclist_add-fix +++ a/fs/proc/kcore.c @@ -63,7 +63,7 @@ static DEFINE_RWLOCK(kclist_lock); static int kcore_need_update = 1; /* This doesn't grab kclist_lock, so it should only be used at init time. */ -void +void __init kclist_add(struct kcore_list *new, void *addr, size_t size, int type) { new->addr = (unsigned long)addr; --- a/include/linux/kcore.h~proc-kcore-dont-grab-lock-for-kclist_add-fix +++ a/include/linux/kcore.h @@ -35,7 +35,7 @@ struct vmcoredd_node { }; #ifdef CONFIG_PROC_KCORE -extern void kclist_add(struct kcore_list *, void *, size_t, int type); +extern void __init kclist_add(struct kcore_list *, void *, size_t, int type); #else static inline void kclist_add(struct kcore_list *new, void *addr, size_t size, int type)