Re: [PATCH 01/34] namespace: take lock_mount_hash() directly when changing flags

From: Christian Brauner <christian.brauner@ubuntu.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Lennart Poettering <lennart@poettering.net>,
	Mimi Zohar <zohar@linux.ibm.com>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	containers@lists.linux-foundation.org,
	Tycho Andersen <tycho@tycho.ws>,
	Miklos Szeredi <miklos@szeredi.hu>,
	smbarber@chromium.org, linux-ext4@vger.kernel.org,
	Mrunal Patel <mpatel@redhat.com>,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Jann Horn <jannh@google.com>,
	selinux@vger.kernel.org, Josh Triplett <josh@joshtriplett.org>,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>,
	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
	Geoffrey Thomas <geofft@ldpreload.com>,
	David Howells <dhowells@redhat.com>,
	John Johansen <john.johansen@canonical.com>,
	Theodore Tso <tytso@mit.edu>,
	Seth Forshee <seth.forshee@canonical.com>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-unionfs@vger.kernel.org,
	linux-security-module@vger.kernel.org, linux-audit@redhat.com,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-api@vger.kernel.org,
	Casey Schaufler <casey@schaufler-ca.com>,
	Alban Crequy <alban@kinvolk.io>,
	linux-integrity@vger.kernel.org, Todd Kjos <tkjos@google.com>
Subject: Re: [PATCH 01/34] namespace: take lock_mount_hash() directly when changing flags
Date: Mon, 2 Nov 2020 14:33:31 +0100	[thread overview]
Message-ID: <20201102133331.66v4hxtmlnjrucnn@wittgenstein> (raw)
In-Reply-To: <20201101144108.GA23378@infradead.org>

On Sun, Nov 01, 2020 at 02:41:08PM +0000, Christoph Hellwig wrote:
> > index cebaa3e81794..20ee291a7af4 100644
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -463,7 +463,6 @@ static int mnt_make_readonly(struct mount *mnt)
> >  {
> >  	int ret = 0;
> >  
> > -	lock_mount_hash();
> 
> What about adding a lockdep_assert_lock_held in all the functions
> that used to take the lock to document the assumptions?

Good idea and will do. I wanted to do this but then didn't because I
haven't seen widespread use of lockdep assert in fs/namespace.c.

> 
> >  static int __mnt_unmake_readonly(struct mount *mnt)
> >  {
> > -	lock_mount_hash();
> >  	mnt->mnt.mnt_flags &= ~MNT_READONLY;
> > -	unlock_mount_hash();
> >  	return 0;
> 
> This helper is rather pointless now.

Ok, will remove.

> 
> >  static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
> >  {
> > -	lock_mount_hash();
> >  	mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
> >  	mnt->mnt.mnt_flags = mnt_flags;
> >  	touch_mnt_namespace(mnt->mnt_ns);
> > -	unlock_mount_hash();
> 
> In linux-next there is an additional notify_mount after the unlock here.

Thanks! I can try rebasing on -next.

> 
> Also while you touch this lock_mount_hash/unlock_mount_hash could be
> moved to namespace.c and maked static now.

Ok, will try to do that.
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