From patchwork Wed Jun 9 08:51:22 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 12309311 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 25D02C47095 for ; Wed, 9 Jun 2021 08:52:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE5156101A for ; Wed, 9 Jun 2021 08:52:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237754AbhFIIyB convert rfc822-to-8bit (ORCPT ); Wed, 9 Jun 2021 04:54:01 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:22648 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231474AbhFIIyB (ORCPT ); Wed, 9 Jun 2021 04:54:01 -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-412-PTv6_32ZMuai4EYYRrW8Ww-1; Wed, 09 Jun 2021 04:52:01 -0400 X-MC-Unique: PTv6_32ZMuai4EYYRrW8Ww-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E0689C7400; Wed, 9 Jun 2021 08:51:59 +0000 (UTC) Received: from web.messagingengine.com (ovpn-116-20.sin2.redhat.com [10.67.116.20]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2F93A5D9DE; Wed, 9 Jun 2021 08:51:40 +0000 (UTC) Subject: [PATCH v6 5/7] 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 , "Eric W. Biederman" , Carlos Maiolino , linux-fsdevel , Kernel Mailing List Date: Wed, 09 Jun 2021 16:51:22 +0800 Message-ID: <162322868275.361452.17585267026652222121.stgit@web.messagingengine.com> In-Reply-To: <162322846765.361452.17051755721944717990.stgit@web.messagingengine.com> References: <162322846765.361452.17051755721944717990.stgit@web.messagingengine.com> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=raven@themaw.net 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(). The last hunk in the patch, applied to kernfs_fill_super(), is possibly not needed but taking the lock was present originally and I prefer to continue to take it so the rb tree is held stable during the call to kernfs_refresh_inode() made by kernfs_get_inode(). Signed-off-by: Ian Kent Reviewed-by: Miklos Szeredi --- 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;