linux-kernel - Re: [PATCH 2/4] vfs: keep list of mounts for each superblock

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Date:	Thu, 04 Aug 2011 11:10:54 +0200
From:	Miklos Szeredi <mszeredi@...e.cz>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Miklos Szeredi <miklos@...redi.hu>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, jack@...e.cz, hch@...radead.org,
	akpm@...ux-foundation.org, toshi.okajima@...fujitsu.com
Subject: Re: [PATCH 2/4] vfs: keep list of mounts for each superblock

On Wed, 2011-08-03 at 23:17 +0100, Al Viro wrote:
> On Wed, Aug 03, 2011 at 12:48:39PM +0200, Miklos Szeredi wrote:
> > @@ -696,6 +696,11 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
> >  	mnt->mnt_sb = root->d_sb;
> >  	mnt->mnt_mountpoint = mnt->mnt_root;
> >  	mnt->mnt_parent = mnt;
> > +
> > +	br_write_lock(vfsmount_lock);
> > +	list_add_tail(&mnt->mnt_instance, &mnt->mnt_sb->s_mounts);
> > +	br_write_unlock(vfsmount_lock);
> 
> Racy.
> 
> > @@ -745,6 +750,10 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
> >  			if (!list_empty(&old->mnt_expire))
> >  				list_add(&mnt->mnt_expire, &old->mnt_expire);
> >  		}
> > +
> > +		br_write_lock(vfsmount_lock);
> > +		list_add_tail(&mnt->mnt_instance, &mnt->mnt_sb->s_mounts);
> > +		br_write_unlock(vfsmount_lock);
> 
> Ditto.  If you expect to be able to find *all* vfsmounts over given sb,
> this locking is simply wrong.

I don't understand.  All accesses to mnt_instance/s_mounts are protected
by vfsmount_lock.  What else is needed?

Thanks,
Miklos


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