linux-kernel - Re: [PATCH 6/9] mnt: simplify ns_common

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Message-ID: <rmf52dxd73wrsdtvqgjoa7i4am42k6i4eesd7nbxvdq7j22xy7@r7jkm4ahv6s7>
Date: Thu, 18 Sep 2025 11:12:54 +0200
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org, 
	Amir Goldstein <amir73il@...il.com>, Josef Bacik <josef@...icpanda.com>, 
	Jeff Layton <jlayton@...nel.org>, Mike Yuan <me@...dnzj.com>, 
	Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, Lennart Poettering <mzxreary@...inter.de>, 
	Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Koutný <mkoutny@...e.com>, Jakub Kicinski <kuba@...nel.org>, 
	Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker <frederic@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH 6/9] mnt: simplify ns_common_init() handling

On Thu 18-09-25 10:15:01, Christian Brauner wrote:
> On Wed, Sep 17, 2025 at 06:45:11PM +0200, Jan Kara wrote:
> > On Wed 17-09-25 12:28:05, Christian Brauner wrote:
> > > Assign the reserved MNT_NS_ANON_INO sentinel to anonymous mount
> > > namespaces and cleanup the initial mount ns allocation. This is just a
> > > preparatory patch and the ns->inum check in ns_common_init() will be
> > > dropped in the next patch.
> > > 
> > > Signed-off-by: Christian Brauner <brauner@...nel.org>
> > 
> > ...
> > > ---
> > >  fs/namespace.c    | 7 ++++---
> > >  kernel/nscommon.c | 2 +-
> > >  2 files changed, 5 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/fs/namespace.c b/fs/namespace.c
> > > index c8251545d57e..09e4ecd44972 100644
> > > --- a/fs/namespace.c
> > > +++ b/fs/namespace.c
> > > @@ -4104,6 +4104,8 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool a
> > >  		return ERR_PTR(-ENOMEM);
> > >  	}
> > >  
> > > +	if (anon)
> > > +		new_ns->ns.inum = MNT_NS_ANON_INO;
> > >  	ret = ns_common_init(&new_ns->ns, &mntns_operations, !anon);
> > >  	if (ret) {
> > >  		kfree(new_ns);
> > > @@ -6020,10 +6022,9 @@ static void __init init_mount_tree(void)
> > >  	if (IS_ERR(mnt))
> > >  		panic("Can't create rootfs");
> > >  
> > > -	ns = alloc_mnt_ns(&init_user_ns, true);
> > > +	ns = alloc_mnt_ns(&init_user_ns, false);
> > >  	if (IS_ERR(ns))
> > >  		panic("Can't allocate initial namespace");
> > > -	ns->ns.inum = PROC_MNT_INIT_INO;
> > >  	m = real_mount(mnt);
> > >  	ns->root = m;
> > >  	ns->nr_mounts = 1;
> > > @@ -6037,7 +6038,7 @@ static void __init init_mount_tree(void)
> > >  	set_fs_pwd(current->fs, &root);
> > >  	set_fs_root(current->fs, &root);
> > >  
> > > -	ns_tree_add(ns);
> > > +	ns_tree_add_raw(ns);
> > 
> > But we don't have ns->ns_id set by anything now? Or am I missing something?
> 
> It is set in alloc_mnt_ns() via ns_tree_gen_id(). :)
> Unless I'm missing something.

Ah, right. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR