From patchwork Mon Jul 11 03:37:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 12912772 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 B8C46C433EF for ; Mon, 11 Jul 2022 03:37:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229682AbiGKDhq (ORCPT ); Sun, 10 Jul 2022 23:37:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38524 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229450AbiGKDho (ORCPT ); Sun, 10 Jul 2022 23:37:44 -0400 Received: from smtp01.aussiebb.com.au (smtp01.aussiebb.com.au [IPv6:2403:5800:3:25::1001]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4656762D3; Sun, 10 Jul 2022 20:37:43 -0700 (PDT) Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp01.aussiebb.com.au (Postfix) with ESMTP id DD50D10052F; Mon, 11 Jul 2022 13:37:41 +1000 (AEST) X-Virus-Scanned: Debian amavisd-new at smtp01.aussiebb.com.au Received: from smtp01.aussiebb.com.au ([127.0.0.1]) by localhost (smtp01.aussiebb.com.au [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id mhwLkaRdPbHE; Mon, 11 Jul 2022 13:37:41 +1000 (AEST) Received: by smtp01.aussiebb.com.au (Postfix, from userid 116) id CAB3910052E; Mon, 11 Jul 2022 13:37:41 +1000 (AEST) Received: from donald.themaw.net (180-150-90-198.b4965a.per.nbn.aussiebb.net [180.150.90.198]) by smtp01.aussiebb.com.au (Postfix) with ESMTP id 2647710051D; Mon, 11 Jul 2022 13:37:41 +1000 (AEST) Subject: [PATCH 1/3] vfs: track count of child mounts From: Ian Kent To: Al Viro Cc: Andrew Morton , David Howells , Miklos Szeredi , linux-fsdevel , Kernel Mailing List Date: Mon, 11 Jul 2022 11:37:40 +0800 Message-ID: <165751066075.210556.17270883735094115327.stgit@donald.themaw.net> In-Reply-To: <165751053430.210556.5634228273667507299.stgit@donald.themaw.net> References: <165751053430.210556.5634228273667507299.stgit@donald.themaw.net> User-Agent: StGit/1.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org While the total reference count of a mount is mostly all that's needed the reference count corresponding to the mounts only is occassionally also needed (for example, autofs checking if a tree of mounts can be expired). To make this reference count avaialble with minimal changes add a counter to track the number of child mounts under a given mount. This count can then be used to calculate the mounts only reference count. Signed-off-by: Ian Kent --- fs/mount.h | 1 + fs/namespace.c | 8 ++++++++ 2 files changed, 9 insertions(+) diff --git a/fs/mount.h b/fs/mount.h index 0b6e08cf8afb..3f0f62912463 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -52,6 +52,7 @@ struct mount { int mnt_writers; #endif struct list_head mnt_mounts; /* list of children, anchored here */ + unsigned int mnt_mounts_cnt; /* count of children, anchored here */ struct list_head mnt_child; /* and going through their mnt_child */ struct list_head mnt_instance; /* mount instance on sb->s_mounts */ const char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */ diff --git a/fs/namespace.c b/fs/namespace.c index e6a7e769d25d..3c1ee5b5bb69 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -882,6 +882,8 @@ static struct mountpoint *unhash_mnt(struct mount *mnt) struct mountpoint *mp; mnt->mnt_parent = mnt; mnt->mnt_mountpoint = mnt->mnt.mnt_root; + if (!list_empty(&mnt->mnt_child)) + mnt->mnt_parent->mnt_mounts_cnt--; list_del_init(&mnt->mnt_child); hlist_del_init_rcu(&mnt->mnt_hash); hlist_del_init(&mnt->mnt_mp_list); @@ -918,6 +920,7 @@ static void __attach_mnt(struct mount *mnt, struct mount *parent) hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mnt->mnt_mountpoint)); list_add_tail(&mnt->mnt_child, &parent->mnt_mounts); + parent->mnt_mounts_cnt++; } /* @@ -936,6 +939,8 @@ void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct m struct mountpoint *old_mp = mnt->mnt_mp; struct mount *old_parent = mnt->mnt_parent; + if (!list_empty(&mnt->mnt_child)) + mnt->mnt_parent->mnt_mounts_cnt--; list_del_init(&mnt->mnt_child); hlist_del_init(&mnt->mnt_mp_list); hlist_del_init_rcu(&mnt->mnt_hash); @@ -1562,6 +1567,8 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how) /* Hide the mounts from mnt_mounts */ list_for_each_entry(p, &tmp_list, mnt_list) { + if (!list_empty(&p->mnt_child)) + p->mnt_parent->mnt_mounts_cnt--; list_del_init(&p->mnt_child); } @@ -1590,6 +1597,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how) if (!disconnect) { /* Don't forget about p */ list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts); + p->mnt_parent->mnt_mounts_cnt++; } else { umount_mnt(p); }