From patchwork Thu Mar 5 05:21:21 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 5943521 Return-Path: X-Original-To: patchwork-linux-fsdevel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 95967BF440 for ; Thu, 5 Mar 2015 05:24:13 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id BBACD202BE for ; Thu, 5 Mar 2015 05:24:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9211202B8 for ; Thu, 5 Mar 2015 05:24:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752696AbbCEFXW (ORCPT ); Thu, 5 Mar 2015 00:23:22 -0500 Received: from cantor2.suse.de ([195.135.220.15]:42180 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752067AbbCEFXT (ORCPT ); Thu, 5 Mar 2015 00:23:19 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 4BBC8AB09; Thu, 5 Mar 2015 05:23:18 +0000 (UTC) From: NeilBrown To: Alexander Viro Date: Thu, 05 Mar 2015 16:21:21 +1100 Subject: [PATCH 7/9] VFS/namei: handle LOOKUP_RCU in page_follow_link_light. Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20150305052121.23906.53544.stgit@notabene.brown> In-Reply-To: <20150305051530.23906.65097.stgit@notabene.brown> References: <20150305051530.23906.65097.stgit@notabene.brown> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP If the symlink has already be been read-in, then page_follow_link_light can succeed in RCU-walk mode. page_getlink_rcu() is added to support this. With this many filesystems can follow links in RCU-walk mode when everything is cached. This includes ext?fs and others. If the page is a HighMem page we do *not* try to kmap_atomic, but simply give up - only page_address() is used. This is because we need to be able to sleep while holding the address of the page, particularly over calls to do_last() which can be quite slow and in particular takes a mutex. If this were a problem, then copying into a GFP_ATOMIC allocation might be a workable solution. Signed-off-by: NeilBrown --- fs/namei.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/fs/namei.c b/fs/namei.c index 11e6b2068c96..48571b2eaa18 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -4468,6 +4468,28 @@ static char *page_getlink(struct dentry * dentry, struct page **ppage) return kaddr; } +/* get the link contents from pagecache under RCU */ +static char *page_getlink_rcu(struct dentry * dentry, struct page **ppage) +{ + char *kaddr; + struct page *page; + struct address_space *mapping = dentry->d_inode->i_mapping; + page = find_get_page(mapping, 0); + if (page && + (!PageUptodate(page) || PageHighMem(page))) { + put_page(page); + page = NULL; + } + if (!page) { + *ppage = ERR_PTR(-ECHILD); + return NULL; + } + *ppage = page; + kaddr = page_address(page); + nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1); + return kaddr; +} + int page_readlink(struct dentry *dentry, char __user *buffer, int buflen) { struct page *page = NULL; @@ -4484,8 +4506,9 @@ void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd) { struct page *page = NULL; if (nd->flags & LOOKUP_RCU) - return ERR_PTR(-ECHILD); - nd_set_link(nd, page_getlink(dentry, &page)); + nd_set_link(nd, page_getlink_rcu(dentry, &page)); + else + nd_set_link(nd, page_getlink(dentry, &page)); return page; } EXPORT_SYMBOL(page_follow_link_light); @@ -4495,7 +4518,8 @@ void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) struct page *page = cookie; if (page) { - kunmap(page); + if (!(nd->flags & LOOKUP_LINK_RCU)) + kunmap(page); page_cache_release(page); } }