From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: Re: [RFC PATCH 2/3] cgroup: Rely on namespace_sem in current_cgns_cgroup_from_root explicitly Date: Tue, 23 May 2023 12:42:46 +0200 Message-ID: <20230523-radar-gleich-781fd4006057@brauner> References: <20230502133847.14570-1-mkoutny@suse.com> <20230502133847.14570-3-mkoutny@suse.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684838572; bh=dAZtfPEcdx8w0xksIc+4VYD58Jm8oMxQ7+S7bRplZvM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Dc34T6TA2Jylxa+Ta17oKWHKcRWTtyg7v2ias+mVnUeGa6ugVmCGvGQBzxYBOBsnB gVR8bMa+mAb/WmZBAJg4ZHPAQ2lJgy5r/HWYoS1qTIWV7SORr49MZxUzhIN2LkQ7k4 h2gCx3ek59wOr/O+LFTOpCQhvbXw+OrWCwXSIAQ4DjUvaJI+cZAOeKsnOOmK+h4inJ bve2yOEnB29XSuZUjPe686uTQO6OQajO+gMeiz429QS1MKh9QXJEuwOs6aTTiroEGa WMKJd1eOsA7UJBH8COgqfZsl7uTMdscQ8GmfjbyYAYj+UqAG2S0CQuIatxOWFZDFTK E692WpXj+M8Mw== Content-Disposition: inline In-Reply-To: <20230502133847.14570-3-mkoutny-IBi9RG/b67k@public.gmane.org> List-ID: Content-Type: text/plain; charset="utf-8" To: Michal =?utf-8?Q?Koutn=C3=BD?= Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Alexander Viro , Tejun Heo , Zefan Li , Johannes Weiner , Dave Chinner , Rik van Riel , Jiri Wiesner On Tue, May 02, 2023 at 03:38:46PM +0200, 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); > +#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 Nope, we're not putting namespace_sem in a header. The code it protects is massively sensitive and it interacts with mount_lock and other locks. This stays private to fs/namespace.c as far as I'm concerned.