From patchwork Fri May 28 06:34:26 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 12286273 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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,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 A298AC47087 for ; Fri, 28 May 2021 06:34:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7EC60613D4 for ; Fri, 28 May 2021 06:34:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234476AbhE1GgP convert rfc822-to-8bit (ORCPT ); Fri, 28 May 2021 02:36:15 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:47267 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234070AbhE1GgK (ORCPT ); Fri, 28 May 2021 02:36:10 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-246-IjXKAfTwPtuLZXkY2JvE8g-1; Fri, 28 May 2021 02:34:32 -0400 X-MC-Unique: IjXKAfTwPtuLZXkY2JvE8g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 245FDFC99; Fri, 28 May 2021 06:34:31 +0000 (UTC) Received: from web.messagingengine.com (ovpn-116-22.sin2.redhat.com [10.67.116.22]) by smtp.corp.redhat.com (Postfix) with ESMTP id E18215C290; Fri, 28 May 2021 06:34:27 +0000 (UTC) Subject: [REPOST PATCH v4 4/5] kernfs: use i_lock to protect concurrent inode updates From: Ian Kent To: Greg Kroah-Hartman , Tejun Heo Cc: Eric Sandeen , Fox Chen , Brice Goglin , Al Viro , Rick Lindsley , David Howells , Miklos Szeredi , Marcelo Tosatti , linux-fsdevel , Kernel Mailing List Date: Fri, 28 May 2021 14:34:26 +0800 Message-ID: <162218366632.34379.11311748209082333016.stgit@web.messagingengine.com> In-Reply-To: <162218354775.34379.5629941272050849549.stgit@web.messagingengine.com> References: <162218354775.34379.5629941272050849549.stgit@web.messagingengine.com> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: themaw.net Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org The inode operations .permission() and .getattr() use the kernfs node write lock but all that's needed is to keep the rb tree stable while updating the inode attributes as well as protecting the update itself against concurrent changes. And .permission() is called frequently during path walks and can cause quite a bit of contention between kernfs node operations and path walks when the number of concurrent walks is high. To change kernfs_iop_getattr() and kernfs_iop_permission() to take the rw sem read lock instead of the write lock an additional lock is needed to protect against multiple processes concurrently updating the inode attributes and link count in kernfs_refresh_inode(). The inode i_lock seems like the sensible thing to use to protect these inode attribute updates so use it in kernfs_refresh_inode(). Signed-off-by: Ian Kent --- fs/kernfs/inode.c | 10 ++++++---- fs/kernfs/mount.c | 4 ++-- 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c index 3b01e9e61f14e..6728ecd81eb37 100644 --- a/fs/kernfs/inode.c +++ b/fs/kernfs/inode.c @@ -172,6 +172,7 @@ static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode) { struct kernfs_iattrs *attrs = kn->iattr; + spin_lock(&inode->i_lock); inode->i_mode = kn->mode; if (attrs) /* @@ -182,6 +183,7 @@ static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode) if (kernfs_type(kn) == KERNFS_DIR) set_nlink(inode, kn->dir.subdirs + 2); + spin_unlock(&inode->i_lock); } int kernfs_iop_getattr(struct user_namespace *mnt_userns, @@ -191,9 +193,9 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns, struct inode *inode = d_inode(path->dentry); struct kernfs_node *kn = inode->i_private; - down_write(&kernfs_rwsem); + down_read(&kernfs_rwsem); kernfs_refresh_inode(kn, inode); - up_write(&kernfs_rwsem); + up_read(&kernfs_rwsem); generic_fillattr(&init_user_ns, inode, stat); return 0; @@ -284,9 +286,9 @@ int kernfs_iop_permission(struct user_namespace *mnt_userns, kn = inode->i_private; - down_write(&kernfs_rwsem); + down_read(&kernfs_rwsem); kernfs_refresh_inode(kn, inode); - up_write(&kernfs_rwsem); + up_read(&kernfs_rwsem); return generic_permission(&init_user_ns, inode, mask); } diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c index baa4155ba2edf..f2f909d09f522 100644 --- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -255,9 +255,9 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k sb->s_shrink.seeks = 0; /* get root inode, initialize and unlock it */ - down_write(&kernfs_rwsem); + down_read(&kernfs_rwsem); inode = kernfs_get_inode(sb, info->root->kn); - up_write(&kernfs_rwsem); + up_read(&kernfs_rwsem); if (!inode) { pr_debug("kernfs: could not get root inode\n"); return -ENOMEM;