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

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Message-ID: <20110803221707.GM2203@ZenIV.linux.org.uk>
Date:	Wed, 3 Aug 2011 23:17:07 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	jack@...e.cz, hch@...radead.org, akpm@...ux-foundation.org,
	toshi.okajima@...fujitsu.com, mszeredi@...e.cz
Subject: Re: [PATCH 2/4] vfs: keep list of mounts for each superblock

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.
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