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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86D5EC77B73 for ; Tue, 2 May 2023 19:52:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229709AbjEBTv7 (ORCPT ); Tue, 2 May 2023 15:51:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229482AbjEBTv5 (ORCPT ); Tue, 2 May 2023 15:51:57 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E26D01FC3 for ; Tue, 2 May 2023 12:51:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683057066; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0u1c/zI7EG5oA8EEQf+n5SVUWPETfw09W7j85YlQyd0=; b=UIzhf4QOQdGbRfkxR8N5VA6fayATpQEEoJsEgl/kE6N1aY8uaDgd3+RYispIBgL6e8XwEF zlYOFjOwUEYw0ZWDlGjdNGyOXPQbDW/chJtQPqecbin434tdK/+voaqnb15sdQhNUJRpEz TTqZVBXgQzZwzBUXeHd5xx1/IpHgsC8= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-116-lQVk6mbDNhe49U8jj1AyhQ-1; Tue, 02 May 2023 15:51:01 -0400 X-MC-Unique: lQVk6mbDNhe49U8jj1AyhQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 401FE1C068C2; Tue, 2 May 2023 19:51:00 +0000 (UTC) Received: from [10.22.10.239] (unknown [10.22.10.239]) by smtp.corp.redhat.com (Postfix) with ESMTP id 563C6492C13; Tue, 2 May 2023 19:50:59 +0000 (UTC) Message-ID: <0beea9a5-a163-75e2-59c2-2b092fe96d16@redhat.com> Date: Tue, 2 May 2023 15:50:59 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [RFC PATCH 2/3] cgroup: Rely on namespace_sem in current_cgns_cgroup_from_root explicitly Content-Language: en-US To: =?UTF-8?Q?Michal_Koutn=c3=bd?= , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Cc: Alexander Viro , Christian Brauner , Tejun Heo , Zefan Li , Johannes Weiner , Dave Chinner , Rik van Riel , Jiri Wiesner References: <20230502133847.14570-1-mkoutny@suse.com> <20230502133847.14570-3-mkoutny@suse.com> From: Waiman Long In-Reply-To: <20230502133847.14570-3-mkoutny@suse.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/2/23 09:38, Michal Koutný wrote: > The function current_cgns_cgroup_from_root() expects a stable > cgroup_root, which is currently ensured with RCU read side paired with > cgroup_destroy_root() called after RCU period. > > The particular current_cgns_cgroup_from_root() is called from VFS code > and cgroup_root stability can be also ensured by namespace_sem. Mark it > explicitly as a preparation for further rework. > > Signed-off-by: Michal Koutný > --- > fs/namespace.c | 5 ++++- > include/linux/mount.h | 4 ++++ > kernel/cgroup/cgroup.c | 7 +++---- > 3 files changed, 11 insertions(+), 5 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 54847db5b819..0d2333832064 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -71,7 +71,10 @@ static DEFINE_IDA(mnt_group_ida); > static struct hlist_head *mount_hashtable __read_mostly; > static struct hlist_head *mountpoint_hashtable __read_mostly; > static struct kmem_cache *mnt_cache __read_mostly; > -static DECLARE_RWSEM(namespace_sem); > +DECLARE_RWSEM(namespace_sem); > +#ifdef CONFIG_LOCKDEP > +EXPORT_SYMBOL_GPL(namespace_sem); I don't think fs/namespace.o and kernel/cgroup/cgroup.o can't be built into a kernel module. I doubt we need to export it. > +#endif > static HLIST_HEAD(unmounted); /* protected by namespace_sem */ > static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */ > > diff --git a/include/linux/mount.h b/include/linux/mount.h > index 1ea326c368f7..6277435f6748 100644 > --- a/include/linux/mount.h > +++ b/include/linux/mount.h > @@ -80,6 +80,10 @@ static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt) > return smp_load_acquire(&mnt->mnt_idmap); > } > > +#ifdef CONFIG_LOCKDEP > +extern struct rw_semaphore namespace_sem; > +#endif > + > extern int mnt_want_write(struct vfsmount *mnt); > extern int mnt_want_write_file(struct file *file); > extern void mnt_drop_write(struct vfsmount *mnt); > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 55e5f0110e3b..32d693a797b9 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -1440,13 +1440,12 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) > > lockdep_assert_held(&css_set_lock); > > - rcu_read_lock(); > + /* namespace_sem ensures `root` stability on unmount */ > + lockdep_assert(lockdep_is_held_type(&namespace_sem, -1)); It will be easier if you just use lockdep_is_held() without the 2nd argment. > > cset = current->nsproxy->cgroup_ns->root_cset; > res = __cset_cgroup_from_root(cset, root); > > - rcu_read_unlock(); > - > return res; > } > > @@ -1454,7 +1453,7 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) > * Look up cgroup associated with current task's cgroup namespace on the default > * hierarchy. > * > - * Unlike current_cgns_cgroup_from_root(), this doesn't need locks: > + * Relaxed locking requirements: > * - Internal rcu_read_lock is unnecessary because we don't dereference any rcu > * pointers. > * - css_set_lock is not needed because we just read cset->dfl_cgrp. Cheers, Longman